In cooperation with the California State Water Resources Control Board 

A product of the California Groundwater Ambient Monitoring and Assessment (GAMA) Program

Groundwater Quality Data for the Tahoe–Martis Study Unit, 

2007: Results from the California GAMA Program

U.S. Department of the Interior

U.S. Geological Survey

Data Series 432
Cover Photographs:

Top: Lake Tahoe shoreline, 2007. (Photograph taken by Cathy M. Munday, U.S. Geological Survey.)

Bottom: Sampling point, 2007. (Photograph taken by Mike Judd, U.S. Geological Survey.)
Groundwater Quality Data for the 

Tahoe–Martis Study Unit, 2007: Results 

from the California GAMA Program

By Miranda S. Fram, Cathy Munday, and Kenneth Belitz

In cooperation with the California State Water Resources Control Board

Data Series 432

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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Suggested citation:

Fram, M.S., Munday, Cathy, and Belitz, Kenneth, 2009, Groundwater quality data for the Tahoe–Martis study unit, 

2007: Results from the California GAMA Program: U.S. Geological Survey Data Series 432, 88 p. Available at 

http://pubs.usgs.gov/ds/432/
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction ....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................4

Hydrogeologic Setting ........................................................................................................................4

Tahoe Study Area.........................................................................................................................7

Martis Study Area........................................................................................................................8

Hard Rock Study Area.................................................................................................................8

Methods ..........................................................................................................................................................8

Study Design..........................................................................................................................................8

Sample Collection and Analysis.........................................................................................................9

Data Reporting.....................................................................................................................................10

Quality Assurance...............................................................................................................................10

Water-Quality Results ................................................................................................................................10

Quality-Control Results ......................................................................................................................10

Comparison Thresholds.....................................................................................................................10

Groundwater Quality Data.................................................................................................................11

Field Water-Quality Indicators.................................................................................................12

Organic Constituents.................................................................................................................12

Inorganic Constituents..............................................................................................................12

Isotopic Tracers .........................................................................................................................13

Radioactive Constituents..........................................................................................................13

Future Work ..................................................................................................................................................14

Summary .......................................................................................................................................................14

Acknowledgments.......................................................................................................................................15

References Cited..........................................................................................................................................15

Tables ...........................................................................................................................................................21

Appendix........................................................................................................................................................60

Appendix Tables...........................................................................................................................................73
iv

Figures

Figure 1. Map of the 10 hydrogeologic provinces of California and the location of the 

 Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) 

 study unit ...................................................................................................................................3

Figure 2. Map of the Tahoe–Martis Groundwater Ambient Monitoring and Assessment 

 (GAMA) study unit, and locations of groundwater basins, major cities, major 

 hydrologic features, and the surface-water watershed area for Lake Tahoe 

 and the Tahoe and Martis Valley groundwater basins, California ...................................5

Figure 3. Map of the northern (A) and southern (B) parts of the Tahoe–Martis 

 Groundwater Ambient Monitoring and Assessment (GAMA) study unit, 

 California, and the distribution of the study area grid cells, and locations 

 of the sampled grid wells and the understanding wells ....................................................6

Tables

Table 1. Well identification, and sampling and construction information for wells 

 sampled for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment 

 (GAMA) study, California, June–September, 2007 .............................................................22

Table 2. Classes of chemical and microbial constituents and water-quality indicators 

 collected for the slow and intermediate sampling schedules for the Tahoe–Martis 

 Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

 June–September, 2007 ...........................................................................................................24

Table 3A. Volatile organic compounds and gasoline additives, primary uses or sources, 

 comparative thresholds, and reporting information for the U.S. Geological Survey 

 (USGS) National Water Quality Laboratory Schedule 2020 ..............................................25

Table 3B. Gasoline oxygenates and degradates, primary uses or sources, comparative 

 thresholds, and reporting information for the U.S. Geological Survey (USGS) 

 National Water Quality Laboratory Schedule 4024 ............................................................28

Table 3C. Pesticides and pesticide degradates, primary uses or sources, comparative 

 thresholds, and reporting information for the U.S. Geological Survey (USGS) 

 National Water Quality Laboratory Schedule 2003 ............................................................29

Table 3D. Pharmaceutical compounds, primary uses or sources, comparative thresholds, 

 and reporting information for the U.S. Geological Survey (USGS) National Water 

 Quality Laboratory schedule 2080 .........................................................................................31

Table 3E. Constituents of special interest, primary uses or sources, comparative 

 thresholds, and reporting information for the Montgomery Watson Harza and 

 Weck Laboratories ..................................................................................................................32

Table 3F. Nutrients and dissolved organic carbon, comparative thresholds, and reporting 

 information for the U.S. Geological Survey (USGS) National Water Quality 

 Laboratory Schedule 2755 ......................................................................................................32

Table 3G. Major and minor ions and trace elements, comparative thresholds, and 

 reporting information for the U.S. Geological Survey (USGS) National Water 

 Quality Laboratory Schedule 1948 ........................................................................................33
v

Table 3H. Arsenic, chromium, and iron species, comparative thresholds, and reporting 

 information for the U.S. Geological Survey (USGS) Trace Metal Laboratory, 

 Boulder, Colorado....................................................................................................................34

Table 3I. Isotopic and radioactive constituents, comparative thresholds, and reporting 

 information for laboratories...................................................................................................35

Table 3J. Noble gases and tritium, comparison thresholds and reporting information 

 for the Lawrence Livermore National Laboratory..............................................................36

Table 3K. Microbial constituents, comparison thresholds, and reporting information 

 for the U.S. Geological Survey (USGS) Ohio Microbiology Laboratory parameter 

 codes 99335 and 99332. ..........................................................................................................36

Table 4. Water-quality indicators in samples collected for the Tahoe–Martis 

 Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

 June–September 2007 ............................................................................................................37

Table 5. Volatile organic compounds (VOC), and gasoline oxygenates and degradates 

 detected in samples collected for the Tahoe–Martis Groundwater Ambient 

 Monitoring and Assessment (GAMA) study, California, June–September 2007 ..........39

Table 6. Pesticides and pesticide degradates detected in samples collected for the 

 Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, 

 California, June–September 2007.........................................................................................40

Table 7. Nutrients detected in samples collected for the Tahoe–Martis Groundwater 

 Ambient Monitoring and Assessment (GAMA) study, California, June–September 

 2007 ............................................................................................................................................41

Table 8. Major and minor ions and dissolved solids detected in samples collected 

 for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment 

 (GAMA) study, California, June–September 2007..............................................................43

Table 9. Trace elements detected in groundwater samples collected for the Tahoe–Martis 

 Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

 June–September 200. .............................................................................................................47

Table 10. Species of inorganic arsenic, iron, and chromium detected in samples collected 

 for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) 

 study, California, June–September 2007 .............................................................................51

Table 11. Stable isotope and strontium isotope ratios and tritium and carbon–14 

 activities detected in samples collected for the Tahoe–Martis Groundwater 

 Ambient Monitoring and Assessment (GAMA) study, California, June–September 

 2007 ............................................................................................................................................53

Table 12A. Uranium isotopes and radon-222 detected in samples collected for the 

 Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, 

 California, June–September 2007.........................................................................................55

Table 12B. Gross alpha and gross beta particle activities detected in samples collected 

 for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) 

 study, California, June-September 2007..............................................................................58

Table 12C. Radium isotopes detected in samples collected for the Tahoe–Martis 

 Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

 June–September 2007 ............................................................................................................59
vi

Appendix Tables

Table A1. Analytical methods used to measure organic, inorganic, and microbial 

 constituents by the U.S. Geological Survey (USGS) National Water Quality 

 Laboratory (NWQL) and other laboratories ........................................................................74

Table A2. Preferred analytical schedules for constituents appearing on multiple 

 schedules for samples collected for the Tahoe–Martis Groundwater Ambient 

 Monitoring and Assessment (GAMA) study, California, June–September 2007 ..........76

Table A3A. Constituents detected in field blanks collected for the Tahoe–Martis 

 Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

 June–September 2007 ............................................................................................................77

Table A3B. Volatile organic compounds (VOC) detected in a field blank analyzed in 

 triplicate and determined to be affected by residual methanol from equipment 

 cleaning.....................................................................................................................................78

Table A4A. Quality-control summary of replicate analyses of organic constituents 

 detected in samples collected for the Tahoe–Martis Groundwater Ambient 

 Monitoring and Assessment (GAMA) study, California, June–September 2007 ..........79

Table A4B. Quality-control summary of replicate analyses of major and minor ions, 

 nutrients, trace elements, and isotope tracers detected in samples collected 

 for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) 

 study, California, June–September 2007 .............................................................................80

Table A4C. Quality-control summary of replicate analyses of radiochemical constituents 

 detected in samples collected for the Tahoe–Martis Groundwater Ambient 

 Monitoring and Assessment (GAMA) study, California, June–September 2007 ..........82

Table A5A. Quality-control summary of matrix-spike recoveries of volatile organic 

 compounds (VOC) and gasoline oxygenates and degradates in samples collected 

 for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) 

 study, California, June–September 2007 .............................................................................83

Table A5B. Quality-control summary of matrix-spike recoveries of pesticides and 

 pesticide degradates in samples collected for the Tahoe–Martis Groundwater 

 Ambient Monitoring and Assessment (GAMA) study, California, 

 June–September 2007 ............................................................................................................85
vii

Abbreviations and Acronyms

AB Assembly Bill (through the California State Assembly)

AL-US action level (USEPA)

CAS Chemical Abstract Service (American Chemical Society)

CSU combined standard uncertainty

D detected in groundwater samples

DBP disinfection by-product

E estimated or having a higher degree of uncertainty

GAMA Groundwater Ambient Monitoring and Assessment program

GPS Global Positioning System

HAL-US lifetime health advisory (USEPA)

HPLC high-performance liquid chromatography

LRL laboratory reporting level

LSD land-surface datum

LT-MDL long-term method detection level

MCL-US maximum contaminant level (USEPA)

MCL-CA maximum contaminant level (CDPH)

MDL method detection limit

MRL minimum reporting level

MU method uncertainty

N Normal (1 equivalent per liter of solution)

na not available

nc sample not collected

NL-CA notification level (CDPH)

NWIS National Water Information System (USGS)

PCFF-GAMA portable computer field forms program designed for GAMA sampling

QC quality control

RPD relative percent difference

RSD relative standard deviation

RSD5-US risk-specific dose at 10–5 (USEPA)

SD standard deviation

SMCL-CA secondary maximum contaminant level (CDPH)

SMCL-US secondary maximum contaminant level (USEPA)

SRL study reporting limit

ssLC sample-specific critical level

TIC tentatively identified compound

TMART Martis study area grid well prefix

TMARTU Martis study area understanding well prefix

TROCK Hard Rock study area grid well prefix

TROCKU Hard Rock study area understanding well prefix
viii

TTAHO Tahoe study area grid well prefix

TTAHOU Tahoe study area understanding well prefix

TT-US treatment technique (USEPA)

US United States

V constituent detected in blanks and therefore excluded from the dataset of 

groundwater quality results

VPDB Vienna Pee Dee Belemnite

VSMOW Vienna Standard Mean Ocean Water

Organizations

CDPH California Department of Public Health

CDWR California Department of Water Resources

USEPA U.S. Environmental Protection Agency

LLNL Lawrence Livermore National Laboratory

MWH Montgomery Watson Harza

NAWQA National Water Quality Assessment (USGS)

NWQL National Water Quality Laboratory (USGS)

SWRCB California State Water Resources Control Board

USGS U. S. Geological Survey

Selected chemical names

CaCO3 calcium carbonate

CO3

–2 carbonate

CO2 carbon dioxide

HCO3

- bicarbonate

MEK methyl ethyl ketone (2-butanone)

MTBE methyl tert-butyl ether

NDMA N-nitrosodimethylamine

PCE perchloroethene

TCE trichloroethene

TDS total dissolved solids

THM trihalomethane

VOC volatile organic compound

Units of measurement

cm3

 STP/g cubic centimeters of gas at standard temperature and pressure (0 degrees 

Celsius and 1 atmosphere of pressure) per gram of water

ft foot (feet)

in inch

ka thousand years

L liter

mg milligram
ix

mg/L milligram per liter (parts per million)

mi mile

mL milliliter

Ma million years

μg/L microgram per liter (parts per billion)

μL microliter

μm micrometer

pCi/L picocurie per liter

per mil per thousand

°C degrees Celsius

δi

E delta notation, the ratio of a heavier isotope of an element (iE) to the more 

common lighter isotope of that element, relative to a standard reference 

material, expressed as per mil

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8×°C) + 32

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L). Milligrams per liter is equivalent to parts per million (ppm) and 

micrograms per liter is equivalent to parts per billion (ppb).
x

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Abstract 

Groundwater quality in the approximately 460-squaremile Tahoe–Martis study unit was investigated in June through 

September 2007 as part of the Priority Basin Project of the 

Groundwater Ambient Monitoring and Assessment (GAMA) 

Program. The GAMA Priority Basin Project was developed in 

response to the Groundwater Quality Monitoring Act of 2001 

and is being conducted by the U.S. Geological Survey (USGS) 

in cooperation with the California State Water Resources Control Board (SWRCB).

The study was designed to provide a spatially unbiased 

assessment of the quality of raw groundwater used for public 

water supplies within the Tahoe–Martis study unit (Tahoe–

Martis) and to facilitate statistically consistent comparisons 

of groundwater quality throughout California. Samples were 

collected from 52 wells in El Dorado, Placer, and Nevada 

Counties. Forty-one of the wells were selected using a spatially distributed, randomized grid-based method to provide 

statistical representation of the study area (grid wells), and 

11 were selected to aid in evaluation of specific water-quality 

issues (understanding wells).

The groundwater samples were analyzed for a large 

number of synthetic organic constituents (volatile organic 

compounds [VOC], pesticides and pesticide degradates, and 

pharmaceutical compounds), constituents of special interest 

(perchlorate and N-nitrosodimethylamine [NDMA]), naturally occurring inorganic constituents (nutrients, major and 

minor ions, and trace elements), radioactive constituents, and 

microbial indicators. Naturally occurring isotopes (tritium, 

carbon-14, strontium isotope ratio, and stable isotopes of 

hydrogen and oxygen of water), and dissolved noble gases 

also were measured to help identify the sources and ages of 

the sampled groundwater. In total, 240 constituents and waterquality indicators were investigated.

Three types of quality-control samples (blanks, replicates, and samples for matrix spikes) each were collected at 

12 percent of the wells, and the results obtained from these 

samples were used to evaluate the quality of the data for the 

groundwater samples. Field blanks rarely contained detectable concentrations of any constituent, suggesting that data for 

the groundwater samples were not compromised by possible 

contamination during sample collection, handling or analysis. 

Differences between replicate samples were within acceptable 

ranges. Matrix spike recoveries were within acceptable ranges 

for most compounds.

This study did not attempt to evaluate the quality of water 

delivered to consumers; after withdrawal from the ground, raw 

water typically is treated, disinfected, or blended with other 

waters to maintain water quality. Regulatory thresholds apply 

to water that is served to the consumer, not to raw groundwater. However, to provide some context for the results, concentrations of constituents measured in the raw groundwater were 

compared with regulatory and nonregulatory health-based 

thresholds established by the U.S. Environmental Protection 

Agency (USEPA) and the California Department of Public 

Health (CDPH), and with aesthetic and technical thresholds 

established by CDPH. Comparisons between data collected 

for this study and drinking-water thresholds are for illustrative 

purposes only and do not indicate of compliance or noncompliance with regulatory thresholds.

The concentrations of most constituents detected in 

groundwater samples from the Tahoe–Martis wells were 

below drinking-water thresholds. Organic compounds (VOCs 

and pesticides) were detected in about 40 percent of the 

samples from grid wells, and most concentrations were less 

than 1/100th of regulatory and nonregulatory health-based 

thresholds, although the conentration of perchloroethene in 

one sample was above the USEPA maximum contaminant 

level (MCL-US). Concentrations of all trace elements and 

nutrients in samples from grid wells were below regulatory 

and nonregulatory health-based thresholds, with five exceptions. Concentrations of arsenic were above the MCL-US in 

20 percent of the samples from grid wells. Gross alpha particle 

activity (MCL-US), boron (CDPH notification level, NL-CA), 

and molybdenum (USEPA lifetime health advisory, HAL-US) 

were each detected above thresholds in two of the samples 

from grid wells, and radon (proposed alternative MCL-US) 

was detected above the threshold in one sample from a grid 

well. Most of the samples from Tahoe–Martis grid wells had 

concentrations of major elements, total dissolved solids, and 

trace elements below the CDPH secondary maximum contaminant levels, nonenforceable thresholds set for aesthetic 

and technical concerns. Fifteen percent of the samples from 

grid wells contained iron, manganese, or total dissolved solids 

at concentrations above these levels.

Groundwater Quality Data for the Tahoe–Martis Study 

Unit, 2007: Results from the California GAMA Program

By Miranda S. Fram, Cathy Munday, and Kenneth Belitz
2 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Introduction 

Groundwater comprises nearly half of the water used 

for public supply in California (Hutson and others, 2004). To 

assess the quality of ambient groundwater in aquifers used for 

public supply and to establish a baseline groundwater quality monitoring program, the State Water Resources Control 

Board (SWRCB), in collaboration with the U.S. Geological 

Survey (USGS) and Lawrence Livermore National Laboratory 

(LLNL), implemented the Groundwater Ambient Monitoring and Assessment (GAMA) Program (http://www.swrcb.

ca.gov/gama). The GAMA program currently consists of three 

projects: GAMA Priority Basin Project, conducted by the 

USGS (http://ca.water.usgs.gov/gama); GAMA Domestic Well 

Project, conducted by the SWRCB; and GAMA Special Studies, conducted by LLNL. 

The SWRCB initiated the GAMA Priority Basin project 

in response to legislative mandates (Supplemental Report of 

the 1999 Budget Act 1999–00 Fiscal Year, and the Groundwater Quality Monitoring Act of 2001 {Sections 10780-10782.3 

of the California Water Code, Assembly Bill 599}) to assess 

and monitor the quality of groundwater used as public supply 

for municipalities in California. The GAMA Priority Basin 

Project is a comprehensive assessment of statewide groundwater quality designed to help better understand and identify 

risks to groundwater resources, and to increase the availability 

of information about groundwater quality to the public. For 

the Priority Basin Project, the USGS, in collaboration with the 

SWRCB, developed the monitoring plan to assess groundwater basins through direct and other statistically reliable sample 

approaches (Belitz and others, 2003; State Water Resources 

Control Board, 2003). Key aspects of the project are interagency collaboration and cooperation with local water agencies and well owners. Local participation in the project is 

entirely voluntary. 

The GAMA Priority Basin Project is unique in California 

because it includes many chemical analyses that are not otherwise available in statewide water-quality monitoring datasets. 

Groundwater samples collected for the project are analyzed for 

a large number of chemical constituents using analytical methods that have much lower detection limits than those required 

by the California Department of Public Health (CDPH). 

These analyses will be especially useful for providing an early 

indication of changes in groundwater quality. In addition, the 

GAMA Priority Basin Project analyzes samples for a suite of 

constituents more extensive than that required by CDPH, and 

for a suite of chemical and isotopic tracers of hydrologic and 

geochemical processes. A broader understanding of groundwater composition will be useful for identifying the natural 

and human factors affecting water quality. Understanding the 

occurrence and distribution of chemical constituents of significance to water quality is important for the long-term management and protection of groundwater resources.

 The range of hydrologic, geologic, and climatic conditions that exist in California must be considered when 

assessing groundwater quality. Belitz and others (2003) partitioned the state into 10 hydrogeologic provinces, each with 

distinctive hydrologic, geologic, and climatic characteristics 

(fig. 1), and representative regions in all 10 provinces were 

included in the project design. Eighty percent of California’s 

approximately 16,000 active and standby public-supply wells 

are located in groundwater basins within these hydrologic 

provinces. These groundwater basins, defined by the California Department of Water Resources (CDWR), generally 

consist of fairly permeable, unconsolidated deposits of alluvial 

or volcanic origin (California Department of Water Resources, 

2003). Groundwater basins were prioritized for sampling on 

the basis of the number of public-supply wells in the basin, 

with secondary consideration given to municipal groundwater 

use, agricultural pumping, the number of formerly leaking 

underground fuel tanks, and pesticide applications within the 

basins (Belitz and others, 2003). In addition, some groundwater basins or groups of adjacent similar basins with relatively 

few public-supply wells were assigned high priority so that all 

hydrogeologic provinces would be represented in the subset of 

basins sampled as part of the project. The 116 priority basins 

were grouped into 35 study units. Some areas outside of the 

defined groundwater basins were included to represent the 20 

percent of public-supply wells not located in the groundwater 

basins. Of the 10 hydrogeologic provinces, the Sierra Nevada 

contains the largest number of public-supply wells outside of 

the mapped groundwater basins. About 97 percent of the total 

area and approximately 85 percent of the public-supply wells 

in the Sierra Nevada are outside of the mapped groundwater 

basins.

Three types of water-quality assessments are being 

conducted using the data collected in each study unit: (1) 

Status: assessment of the current quality of the groundwater 

resource, (2) Trends: detection of changes in groundwater 

quality, and (3) Understanding: identification of the natural 

and human factors affecting groundwater quality (Kulongoski 

and Belitz, 2004). This report is one in a series of reports 

presenting water-quality data collected in each study unit 

(Wright and others, 2005; Bennett and others, 2006; Kulongoski and others, 2006; Fram and Belitz, 2007; Kulongoski 

and Belitz, 2007; Dawson and others, 2008; Ferrari and others, 

2008; Landon and Belitz, 2008; Mathany and others, 2008; 

Shelton and others, 2008; Schmitt and others, 2008). Subsequent reports will address the status, trends, and understanding 

aspects of the water-quality assessments.

The Tahoe–Martis GAMA study unit, hereinafter referred 

to as Tahoe–Martis, consists of two groundwater basins and 

the areas outside of the basins corresponding to the surfacewater watershed areas for the basins and Lake Tahoe. The 

Tahoe–Martis study was considered high priority to provide 

adequate representation of the Sierra Nevada hydrogeologic 

province (Belitz and others, 2003). 
Introduction 3

Sacramento

Redding

Los Angeles

Bakersfield

San Diego 0 50 100 200 MILES

0 100 200 KILOMETERS 50

Shaded relief derived from U.S. Geological Survey Provinces from Belitz and others, 2003

National Elevation Dataset, 2006 

Albers Equal Area Conic Projection

124° 122° 120° 118° 116° 114°

42°

40°

38°

36°

34°

32°

Transverse

and Selected

Peninsular Range

Desert

Southern

Coast

Ranges

Basin

and Range

Sierra

Nevada

Central

Valley

Modoc

Plateau and

Cascades

Klamath

Mountains

Northern

Coast

Ranges

San

Diego

MEXICO

ARIZONA

NEVADA

OREGON

Tahoe-Martis

Study Unit

Pacific

Ocean

San Francisco

Figure 1. The 10 hydrogeologic provinces of California and the location of the Tahoe–Martis Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit (modified from Belitz and others, 2003).
4 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Purpose and Scope

The purposes of this report are (1) to describe the study 

design and study methods, (2) to present the results of qualitycontrol tests, and (3) to present the analytical results for 

groundwater samples collected in Tahoe–Martis. Groundwater 

samples were analyzed for organic, inorganic, and microbial 

constituents, field parameters, and isotopic tracers. The chemical and microbial data presented in this report were evaluated 

by comparing these data to State and Federal drinking-water 

regulatory and nonregulatory health-based standards that are 

applied to treated drinking water. Thresholds considered for 

this report were those established by the United States Environmental Protection Agency (USEPA) and CDPH. The data 

presented in this report are intended to characterize the quality 

of untreated, raw groundwater resources within the study unit, 

not the treated drinking water delivered to consumers by water 

purveyors. Discussion of the factors that influence the distribution and occurrence of the constituents detected in groundwater samples will be the subject of 

subsequent publications.

Hydrogeologic Setting 

The Tahoe–Martis study unit (Tahoe–Martis) covers 

approximately 460 square miles in El Dorado, Placer, and 

Nevada Counties, California, in the northeast part of the 

Sierra Nevada hydrogeologic province (figs. 1, 2). The study 

unit includes two groundwater basins, as defined by CDWR 

(California Department of Water Resources, 2003). The Tahoe 

Valley groundwater basin is around the shores of Lake Tahoe 

(South, West, and North subbasins), and the Martis Valley 

groundwater basin is north of Lake Tahoe (fig. 2). The study 

unit area is defined by the boundaries of the surface-water 

watersheds of Lake Tahoe and of the Martis Valley groundwater basin, and by the California-Nevada state line. The 

headwaters of the Truckee River are at the southern end of the 

study unit, above the apex of the South Tahoe subbasin, and 

the river flows north into Lake Tahoe. The Truckee River exits 

Lake Tahoe at Tahoe City, flows north out of the Lake Tahoe 

watershed, and then crosses the Martis Valley basin.

Lake Tahoe and the Tahoe Valley and the Martis Valley 

groundwater basins lie in a structural valley between the Sierra 

Nevada crest to the west and the Carson Range to the east. 

The valley was formed by extensional faulting that resulted in 

approximately 5,000 ft of uplift of the Sierra Nevada crest and 

Carson Range relative to the valley in the graben between the 

two mountain ranges. Most of the uplift occurred in the Pliocene and early Pleistocene (2 to 5 million years [Ma]; Birkeland, 1963), although motion on faults around Lake Tahoe 

has continued through the late Pleistocene and Holocene to 

the present (Kent and others, 2005). The bedrock in the Lake 

Tahoe area is primarily composed of Mesozoic (80 to 120 Ma) 

granitic rocks, mostly granodiorites, of the Sierra Nevada 

batholith. Included within the granitic rocks are scattered 

remnants of the older metamorphic rocks into which the granitic plutons intruded. Uplift of the Sierra Nevada and Carson 

Range was accompanied by volcanic activity. Thick sequences 

of late Miocene to Pleistocene (1 to 10 Ma) volcanic rocks 

cover the granitic bedrock in the Martis basin and watershed 

area, and in the Lake Tahoe watershed north of approximately 

the Placer-El Dorado county line (fig. 2). The older volcanic 

rocks are dominated by andesite tuffs, breccias, and flows, and 

the younger rocks by basalt and latite flows and cinder cones. 

Lake Tahoe is impounded by a dam of lava flows. 

The Lake Tahoe and Truckee areas preserve evidence 

of four major glacial advances during the Pleistocene (Birkeland, 1964). The topography of the Tahoe Valley subbasins 

and Martis Valley basin is dominated by glacial moraines and 

outwash plains, primarily from the Tahoe (70 to 150 thousand 

years [ka]) and Tioga (19 to 26 ka) glaciations. The glaciers 

also formed ice dams that episodically raised the level of the 

lake as much as 600 ft above the current lake level, as evidenced by wave-cut terraces high on the mountains around the 

lake. 

The climate in Tahoe–Martis is characterized by warm, 

dry summers and cold, wet winters, although the temperatures 

and precipitation are strongly controlled by altitude and distance from the crest of the Sierra Nevada. The average surface 

altitude of Lake Tahoe is 6,225 ft and the lowest area in the 

Martis basin is 5,700 ft. The mountains bounding the South 

Tahoe subbasin rise to over 9,500 ft. Annual precipitation at 

stations in Truckee and on the California shores of Lake Tahoe 

averages 30–35 inches per year (note that snowfall has been 

converted to equivalent inches of rainfall) (California Department of Water Resources, 2008; Western Regional Climate 

Center, 2008), and precipitation increases to an average of 

over 80 inches per year at the highest elevations on the western side of the Lake Tahoe watershed (Crippen and Pavelka, 

1970). At Lake Tahoe, approximately half of the precipitation falls as snow, and at the highest elevations, nearly all the 

precipitation falls as snow. Ninety percent of the precipitation 

falls in the winter, between October and April (California 

Department of Water Resources, 2008; Western Regional 

Climate Center, 2008).

Tahoe–Martis is divided into three study areas: the Martis 

study area, the Tahoe study area, and the Hard Rock study area 

(fig. 3). The boundary of the Martis study area corresponds 

to the CDWR Martis Valley basin (California Department 

of Water Resources, 2006), and the boundaries of the Tahoe 

study area correspond to the South, West, and North subbasins 

of the CDWR Tahoe Valley basin (California Department of 

Water Resources, 2004a,b,c). The Hard Rock study area corresponds to the surface-water watersheds surrounding the Martis 

and Tahoe Valley basins and Lake Tahoe. 
Introduction 5

Figure 2. The Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study unit, and locations of groundwater 

basins, major cities, major hydrologic features, and the surface-water watershed area for Lake Tahoe and the Tahoe and Martis Valley 

groundwater basins, California.

Truckee

Tahoe City

Truckee River

Rubicon River

South Fork American River

Lake

Tahoe

SIERRA COUNTY

NEVADA COUNTY

NEVADA COUNTY

PLACER COUNTY

PLACER COUNTY

ELDORADO COUNTY

ELDORADO COUNTY

ALPINE COUNTY

AMADOR

 COUNTY

NEVADA

120° 15'

39° 15'

38° 45'

39°

120°

South 

Lake

Tahoe

Meyers

Fallen

Leaf

Lake

Donner

Lake

Upper Truckee River

0 4 8 2 MILES

0 4 82 KILOMETERS

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Sierra Nevada

Carson Range 

Figure 3A

Figure 3B

EXPLANATION

California Department of 

Water Resources groundwater 

basins

Hydrologic Features

Martis Valley

Tahoe Valley

Watershed

Lakes

Rivers
6 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Figure 3. The northern (A) and southern (B) parts of the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) 

study unit, California, and the distribution of the study area grid cells, and locations of the sampled grid wells and the understanding 

wells.

Lake

Tahoe

Donner

Lake

Rubicon River

TMART-05

TMART-08

TMART-06 TMART-07

TMART-13 TMARTU-01 TMART-14

TMART-06

TMART-04 TMART-11 TMART-07

TROCK-12

TROCKU-02

TTAHO-02

TTAHO-05

TROCK-06

TROCK-05

TMART-08

TMART-09 MART-09

TROCK-07

TTAHO-03

TMART-11

TMART-12 MART-12

TTAHO-01

TMART-13

TMART-14 TMARTU-01

TROCK-03 TROCK-03

TROCK-04 ROCK-04

TMART-04

TROCK-07

TROCK-10 ROCK-10

TROCK-12

TROCK-13 ROCK-13

TMART-10

TROCKU-01 ROCKU-01

TROCK-01 TROCK-01

TROCKU-02

TTAHO-01

TTAHO-02

TTAHO-03

TROCK-05 TTAHO-05

TROCK-06

TMART-05

TMART-03

TMART-01 TMART-01

TMART-10 TMART-02 TMART-02

TTAHO-04 TTAHO-04

PLACER COUNTY

NEVADA COUNTY

PLACER COUNTY

ELDORADO COUNTY

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

39° 25'

120° 15' 120° 10' 120° 5'

39° 20'

39° 15'

39° 10'

39° 5'

39°

Prosser Boca Reservoir

Creek

Reservoir

North Fork American River

Truckee Rive

M

r

iddle Fork

American River

EXPLANATION

Martis study area

Tahoe study area

Hard Rock study area

Understanding well

Grid well

Lakes

Rivers

Randomized sampling

 grid cell

TMART-01

TMART-02

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

0 2 4 8 MILES

0 2.5 5 10 KILOMETERS
Introduction 7

Tahoe Study Area

The groundwater-bearing units in the South, West, and 

North subbasins of the Tahoe Valley basin consist of Pliocene 

to Recent glacial, lacustrine, and fluvial deposits, referred to 

as basin-fill deposits (Burnett, 1971; California Department of 

Water Resources, 2004a,b,c). The predominant sediments in 

the basins are glacial outwash sediments that were deposited 

on prograding deltas as the glaciers retreated. The outwash 

sediments are composed of sorted, stratified material; the grain 

size ranges from boulders to fine silt. Glacial tills were also 

deposited in lateral and terminal moraines. In the South Tahoe 

subbasin, the sediments were derived primarily from the 

granitic rocks in the surrounding Sierra Nevada and Carson 

Ranges. Fluctuations in the level of Lake Tahoe during the 

glacial period resulted in interbedding of lacustrine and glacial 

deposits. The lacustrine deposits range from beach sands 

to silt and clay layers. The fine-grained lacustrine deposits 

constitute discontinuous confining layers within the basin fill. 

The relatively thin Holocene fluvial deposits in the modern 

stream channels do not contribute significantly to groundwater 

storage in the basins.

The basin-fill deposits generally are 50 to 150 ft thick in 

the South Tahoe subbasin, but thicknesses up to 1,600 ft have 

been measured near the city of South Lake Tahoe (California 

Department of Water Resources, 2006a). Sediment thicknesses 

in the North and West Tahoe subbasins are less well known, 

but are thought to range from 20 to as much as 200 ft (California Department of Water Resources, 2006b,c). Groundwater conditions range from unconfined to semi-confined to 

confined.

Groundwater is recharged primarily by infiltration of 

rain and snow melt. Recharge occurs through the surface of 

the basin-fill deposits, and from higher elevations through 

fractures and faults in the bedrock and surface soils (Thodal, 

1997). Stream-flow characteristics of the Upper Truckee River 

and Trout Creek in the South Tahoe subbasin suggests that 

these streams are net “gaining” streams, receiving groundwater discharge as they traverse the subbasin (Rowe and 

Allander, 2000).

Figure 3. Continued.

TROCK-02

TROCK-11 TTAHO-06

TTAHO-14

TROCK-09

TROCK-02

TROCK-08 TROCK-08

TROCK-09

TROCK-11 TTAHO-06

TTAHO-08 TAHO-08

TTAHO-09 TAHO-09 TTAHOU-02

TTAHO-11 TTAHO-11

TTAHO-14

TTAHO-07 TTAHO-10

TTAHO-12

TTAHOU-01 TAHOU-01

TTAHOU-02

TTAHOU-03 TTAHOU-03

TTAHOU-04 TTAHOU-04

TTAHO-12

TTAHO-10 TTAHO-07

TTAHOU-08

TTAHO-13

TTAHOU-07

TTAHOU-06

TTAHOU-05

TTAHOU-08

TTAHO-13

TTAHOU-07

TTAHOU-06

TTAHOU-05

ALPINE COUNTY

EL DORADO COUNTY

120° 05' 120° 119° 55'

38° 55'

38° 50'

South Fork American River

West Fork C arson River

Lake

Tahoe

Upper Truckee River

Fallen

Leaf

Lake

Echo

Lake

EXPLANATION

Tahoe study area

Hard Rock study area

Understanding well

Grid well

Lakes

Rivers

TMART-01

TMART-02

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

0 1.5 3 6 MILES

0 2 4 8 KILOMETERS

NEVADA
8 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Martis Study Area

The groundwater bearing units in the Martis Valley basin 

consist of interlayered volcanic and sedimentary deposits 

of late Miocene to late Pleistocene age (less than 1 to 7 Ma) 

(Nimbus Engineers, 2001; California Department of Water 

Resources, 2006). The sedimentary deposits are composed 

of glacial, lacustrine, and fluvial deposits with depositional 

characteristics similar to those of the basin-fill sedimentary 

deposits in the Tahoe Valley subbasins. The primary source of 

sediment deposited in the Martis Valley basin was the andesitic volcanic and volcaniclastic units located in and around the 

basin. The glacial outwash sediments that cover approximately 

half of the surface of the Martis Valley are up to 150 ft thick 

(Birkeland, 1964). The volcanic units include andesite lava, 

tuff, breccias, and volcaniclastic deposits. 

The water-bearing sedimentary and volcanic units are 

up to 1,200 ft thick and are underlain by low-permeability 

Miocene volcanic rocks. The stratigraphy of the basin is complex, but it is generally separated into upper and lower aquifer 

systems that appear to have limited interconnection (Nimbus 

Engineers, 2001). Groundwater recharge occurs primarily by 

infiltration of rain and snow melt in the basin and in the 

mountains surrounding the basin. 

Hard Rock Study Area

The groundwater bearing units in the Hard Rock study 

area are the Mesozoic granitic rocks in the mountains 

surrounding the South Tahoe subbasin and the southern half 

of the West Tahoe subbasin, and the Miocene to Pleistocene 

volcanic rocks in the mountains surrounding the Martis Valley, 

the North Tahoe subbasin, and the northern half of the West 

Tahoe subbasin. Extensive faulting associated with the uplift 

of the Sierra Nevada crest west and the Carson range east of 

the structural valley containing Lake Tahoe and the Tahoe and 

Martis Valley groundwater basins likely contributes to the 

permeability of the granitic and volcanic rocks. 

Methods 

Methods used for the GAMA program were selected 

to achieve the following objectives: (1) design a sampling 

plan suitable for statistical analysis, (2) collect samples in a 

consistent manner statewide, (3) analyze samples using proven 

and reliable laboratory methods, (4) assure the quality of the 

groundwater data, and (5) maintain data securely and with 

relevant documentation. The Appendix to this report contains 

detailed descriptions of the sample collection protocols and 

analytical methods, the quality-control design, and the results 

of analyses of quality-control samples.

Study Design

The wells selected for sampling in this study reflect the 

combination of two well-selection strategies. Forty-one wells 

were selected to provide a statistically unbiased, spatially 

distributed assessment of the quality of groundwater resources 

used for public drinking-water supply, and 11 additional wells 

were selected to provide greater sampling density in several 

areas to aid in the understanding of specific groundwater 

quality issues in the study unit.

The spatially distributed wells were selected using a 

randomized grid-based method (Scott, 1990). The Tahoe and 

the Martis study areas were each divided into 15 equal-area 

cells, approximately 2.5 mi2 and 4 mi2 in area, respectively 

(fig. 3). The Hard Rock study area had relatively few publicsupply wells, and these wells were not evenly distributed. To 

minimize the number of cells without any wells, only the parts 

of the Hard Rock study area near public-supply wells were 

included in the gridded area. Locations of wells listed in the 

statewide database maintained by the CDPH were plotted, and 

1.86-mi (3-kilometer) radius circles were drawn around each 

well. The collective area encompassed by the circles was then 

divided into 15 equal area cells, each approximately 12 mi2

 in 

area (fig. 3). The cell areas in the Tahoe and the Martis study 

areas were smaller than the GAMA design objective of 10-mi2

grid cells in basins outside of the Central Valley hydrogeologic 

province (Belitz and others, 2003). The smaller cell sizes were 

necessary to provide a minimum of 15 cells in each study area 

for statistical confidence.

The objective was to select one public-supply well per 

grid cell. In the Hard Rock study area, approximately onequarter of the public-supply wells listed in the CDPH databases were actually springs. For convenience, all sites will be 

referred to as wells unless the difference between a well and 

a spring is important to the discussion. Forty-one of the 45 

grid cells were sampled; the other 4 grid cells did not contain accessible wells. If a grid cell contained more than one 

public-supply well, each well was randomly assigned a rank. 

The highest ranking well that met basic sampling criteria (for 

example, sampling point located before treatment, capability 

to pump for several hours, and available well-construction 

information) and for which permission to sample could 

be obtained was then sampled. If a grid cell contained no 

accessible public-supply wells, then domestic and irrigation 

wells were considered for sampling. An attempt was made to 

select domestic and irrigation wells with depths and screened 

intervals similar to those in public-supply wells in the area. 

Wells sampled as part of the spatially distributed, randomized 

grid-cell network are hereinafter referred to as grid wells. Grid 

wells in each study area were numbered in the order of sample 

collection, and prefixes were assigned to indicate the study 

area: TTAHO for the Tahoe study area, TMART for the Martis 

study area, and TROCK for the Hard Rock study area (fig. 3, 

table 1). 
Methods 9

Additional wells were sampled to increase sampling density in selected areas and therefore aid in the understanding of 

changes in water chemistry along selected groundwater flow 

paths or between shallow and deep parts of the aquifers. These 

additional wells were not included in the statistical characterization of water quality in Tahoe–Martis because their inclusion would have caused some cells to be overrepresented. 

These additional, non-randomized wells were numbered in 

the order of sample collection and were assigned the prefixes 

TTAHOU, TMARTU, and TROCKU (“U” indicating “understanding”) (fig. 3). 

Table 1 provides the GAMA alphanumeric identification 

number for each well, along with the date sampled, sampling 

schedule, well elevation, well type, and well-construction 

information. Wells classified as production wells have pumps 

that pump the groundwater from the aquifer to a distribution system. Wells classified as monitoring wells included 

short-screen wells installed specifically as monitoring wells 

and wells that were once production wells, but no longer 

have pumps. Monitoring wells were sampled using a portable 

submersible pump. Wells were classified as springs if groundwater could flow from the aquifer into the distribution system 

without a pump, and the well was either drilled horizontally 

or had no drilled hole. The wells were sampled during June 

through September, 2007. The 41 grid wells included 37 sites 

classified by CDPH as public-supply wells (or springs). 

Public-supply wells are not identified in table 1 because of 

security and confidentiality requirements; the number of 

public-supply wells in the grid-well network is reported to 

demonstrate that the network is representative of the parts of 

the aquifers in the study unit that are used for public supply. 

One short-screen monitoring well (TTAHO-13) was used as a 

grid well because the cell contained no other accessible wells, 

and the monitoring well was screened within the same depth 

zone as the public-supply wells in the area. The three remaining grid wells that were not public-supply wells were also 

screened within similar depth zones as public-supply wells in 

their vicinities. The 11 understanding wells included 4 shortscreen monitoring wells, 6 wells classified as public-supply 

wells, and 1 irrigation well. 

Well locations and identifications were verified using 

GPS, 1:24,000 scale USGS topographic maps, existing well 

information in USGS and CDPH databases, and information provided by well owners. Driller’s logs for wells were 

obtained when available. Well information was recorded by 

hand on field sheets, and electronically using specialized software on field laptop computers. All information was verified 

and then uploaded into the USGS National Water Information 

System (NWIS). Well owner information is confidential. Well 

location information and all chemical data are currently inaccessible from NWIS’s public website.

The wells in Tahoe–Martis were sampled using a tiered 

analytical approach. All wells were sampled for a standard 

set of constituents, including field water-quality parameters, 

organic constituents (VOCs and pesticides), perchlorate, 

inorganic constituents (nutrients, major ions, trace elements, 

and trace element species), radioactive constituents (uranium 

isotopes and radon), and geochemical and age dating tracers 

(stable isotopes of hydrogen and oxygen of water, strontium 

isotopes, carbon isotopes, dissolved noble gases, and tritium). 

The standard set of constituents was termed the intermediate

schedule (table 2). Wells on the slow schedule were sampled 

for all the constituents on the intermediate schedule plus field 

alkalinity, pharmaceutical compounds, N-nitrosodimethylamine (NDMA), radium isotopes, gross alpha and gross beta 

particle activities, and microbial constituents. Intermediate

and slow refer to the time required to sample the well for all 

the constituents on the schedule. In Tahoe–Martis, two wells 

could be sampled in one day. Many of the other GAMA study 

units have had a shorter list of standard constituents and have 

termed the standard set the fast schedule because three or four 

fast wells could be sampled in one day. In Tahoe–Martis, 42 

of the groundwater wells were sampled on the intermediate

schedule and 10 on the slow schedule.

Sample Collection and Analysis

Samples were collected in accordance with the protocols 

established by the USGS National Water Quality Assessment 

(NAWQA) program (Koterba and others, 1995) and the USGS 

National Field Manual (U.S. Geological Survey, variously 

dated). These sampling protocols ensure that a representative 

sample of groundwater is collected at each site and that potential contamination of samples during collection and handling is 

minimized. The methods used to collect samples are described 

in the Appendix section “Sample Collection and Analysis.”

Tables 3A–K list the compounds analyzed in each constituent class. Groundwater samples were analyzed for 85 VOCs 

(table 3A); 8 gasoline oxygenates and degradates (Tahoe study 

area only, table 3B); 63 pesticides and pesticide degradates 

(table 3C); 14 pharmaceutical compounds (table 3D); 2 constituents of special interest (table 3E); 5 nutrients (table 3F); 

10 major and minor ions, and total dissolved solids (table 3G); 

24 trace elements (table 3G); arsenic, iron, and chromium 

species (table 3H); stable isotopes of hydrogen and oxygen of 

water, strontium isotopes, carbon isotopes, and 10 radioactive 

constituents, including tritium and carbon-14 (table 3I); 5 dissolved noble gases, and helium stable isotope ratios (table 3J); 

and 2 microbial constituents (table 3K). The methods used for 

sample analysis are described in the Appendix section “Sample 

Collection and Analysis.”
10 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Data Reporting

The methods and conventions used for reporting the data 

are described in the Appendix. Five VOCs analyzed in this 

study were measured by more than one method at the USGS 

National Water Quality Laboratory (NWQL), but only the 

results from the preferred method are reported (see Appendix

section “Constituents on Multiple Analytical Schedules”). 

Arsenic, iron, and chromium concentrations and tritium activities were measured by more than one laboratory, and both sets 

of results are reported for these constituents. 

Quality Assurance

The quality-assurance and quality-control procedures 

used for this study followed the protocols used by the USGS 

NAWQA program (Koterba and others, 1995) and described 

in the USGS National Field Manual (U.S. Geological Survey, 

variously dated). The quality assurance plan followed by the 

NWQL, the primary laboratory used to analyze samples for 

this study, is described by Maloney (2005) and Pirkey and 

Glodt (1998). Quality-control (QC) samples collected in the 

Tahoe–Martis study unit included source-solution blanks, 

field blanks, replicates, and matrix and surrogate spikes. QC 

samples were collected to evaluate potential contamination, 

bias, or variability of the data that may have resulted from 

collecting, processing, storing, transporting, and analyzing 

the samples. Quality-control procedures and quality-control 

sample results are described in the Appendix section “Quality 

Assurance.”

Water-Quality Results 

Quality-Control Results

Results of quality-control analyses (blanks, replicates, 

matrix spikes, and surrogates) were used to evaluate the 

quality of the data for the groundwater samples. On the basis 

of detections in field blanks collected for this and previous 

GAMA study units, detections reported by the laboratory for 

three organic compounds were considered suspect and therefore were removed from the set of groundwater quality data 

presented in this report (see table A3A and additional discussion in Appendix). Results from the replicates confirm that the 

procedures used to collect and analyze the samples were consistent. Ninety-seven percent of the replicate pairs analyzed 

for constituents detected in samples had variability between 

values within acceptable limits; additional discussion can be 

found in the Appendix. Median matrix-spike recoveries for 12 

of the 166 organic constituents analyzed were lower than the 

acceptable limits (table 3C), which may indicate that these 

constituents might not have been detected in some samples if 

their concentrations in these samples had been near the LRLs. 

The quality-control results are described in the Appendix

section “Quality-Control Results”.

Comparison Thresholds

Concentrations of constituents detected in groundwater 

samples were compared with CDPH and USEPA drinkingwater regulatory and nonregulatory health-based thresholds 

and thresholds established for aesthetic purposes (California 

Department of Public Health, 2008a,b; U.S. Environmental 

Protection Agency, 2008a,b,c). The chemical and microbial 

data presented in this report are meant to characterize the quality of the untreated groundwater resources within Tahoe–Martis, and are not intended to represent the treated drinking water 

delivered to consumers by water purveyors. The chemical and 

microbial composition of treated drinking water may differ 

from that of untreated groundwater because treated drinking 

water may be disinfected, filtered, mixed with other waters, 

and exposed to the atmosphere before being delivered to consumers. Comparisons between concentrations of constituents 

in raw, untreated groundwater and drinking-water thresholds 

are for illustrative purposes only, and are not indicative of 

compliance or noncompliance with drinking-water regulations.

The following thresholds were used for comparisons:

• MCL—Maximum Contaminant Level. Legally 

enforceable standards that apply to public water 

systems and are designed to protect public health by 

limiting the levels of contaminants in drinking water. 

MCLs established by the USEPA are the minimum 

standards with which states are required to comply, and 

individual states may choose to set more stringent standards. CDPH has established MCLs for constituents 

not regulated by the USEPA, as well as lowered the 

threshold concentration for a number of constituents 

with MCLs established by the USEPA. In this report, a 

threshold set by the USEPA and adopted by CDPH is 

labeled “MCL-US”, and one set by CDPH that is more 

stringent than the MCL-US is labeled “MCL-CA”. 

CDPH is notified when constituents are detected at 

concentrations greater than an MCL-US or MCL-CA 

thresholds in samples collected for the GAMA Priority 

Basin Project, but these detections do not constitute 

violations of CDPH regulations.

• AL—Action Level. Legally enforceable standards that 

apply to public water systems and are designed to protect public health by limiting the levels of copper and 

lead in drinking water. Detections of copper or lead at 

concentrations above the action-level thresholds trigger 

requirements for mandatory water treatment to reduce 

the corrosiveness of water to water pipes. The action 

levels established by the USEPA and CDPH currently 

are the same; thus the thresholds are labeled “AL-US” 

in this report.
Water-Quality Results 11

• TT – Treatment Technique. Legally enforceable 

standards that apply to public-water systems and are 

designed to protect public health by limiting the levels 

of microbial constituents in drinking water. Detections 

of microbial constituents at abundances above the 

treatment-technique thresholds trigger requirements for 

mandatory additional disinfection during water treatment. The action levels established by the USEPA and 

CDPH are the same; thus the thresholds are labeled 

“TT-US” in this report.

• SMCL – Secondary Maximum Contaminant Level. 

Nonenforceable standards applied to constituents that 

affect the aesthetic qualities of drinking water, such as 

taste, odor, and color, or technical qualities of drinking 

water, such as scaling and staining. Both the USEPA 

and CDPH define SMCLs, but unlike MCLs, SMCLs 

established by CDPH are not required to be at least 

as stringent as those established by USEPA. SMCLs 

established by CDPH (SMCL-CA) are used in this 

report for all constituents that have SMCL-CA values. 

The SMCL-US is used for pH because no SMCL-CA 

has been defined.

• NL—Notification Level. Health-based notification 

levels established by CDPH for some of the constituents in drinking water that lack MCLs (NL-CA). If a 

constituent is detected above its NL-CA, California 

state law requires timely notification of local governing 

bodies and recommends consumer notification.

• HAL—Lifetime Health Advisory Level. The maximum concentration of a constituent at which its presence in drinking water is not expected to cause any 

adverse carcinogenic effects for a lifetime of exposure. 

HALs are established by the USEPA (HAL-US) and 

are calculated assuming consumption of 2 liters (2.1 

quarts) of water per day over a 70-year lifetime by a 

70-kilogram (154-pound) adult and that 20 percent of a 

person’s exposure comes from drinking water.

• RSD5—Risk-Specific Dose. The concentration of 

a constituent in drinking water corresponding to an 

excess estimated lifetime cancer risk of 1 in 100,000. 

RSD5 is an acronym for risk-specific dose at 10–5. 

RSD5s are calculated by dividing the 10–4 cancer 

risk concentration established by the USEPA by ten 

(RSD5-US). USEPA generally only accepts cancer risk 

policies from the States that are based on risk-specific 

doses of 10–5 or smaller (Toccalino and others, 2003).

For constituents having MCLs, the concentrations in 

groundwater samples were compared to the MCL-US or 

MCL-CA. Constituents with SMCLs were compared with the 

SMCL-CA. For chloride, sulfate, specific conductance, and 

total dissolved solids, CDPH defines a “recommended” and 

an “upper” SMCL-CA; concentrations of these constituents 

in groundwater samples were compared with both levels. 

The SMCL-US values for these constituents correspond to 

the recommended SMCL-CA. Detected concentrations of 

constituents that lack an MCL or SMCL were compared to 

the NL-CA. For constituents that lack an MCL, SMCL, or 

NL-CA, detected concentrations were compared with the 

HAL-US. For constituents that lack an MCL, SMCL, NL-CA, 

or HAL-US, detected concentrations were compared with the 

RSD5-US. Note that if a constituent has more than one type of 

established threshold, using this hierarchy to select the comparison threshold will not necessarily result in selecting the 

threshold with the lowest concentration. For example, zinc has 

an SMCL-CA of 5,000 μg/L and a HAL-US of 2,000 μg/L, 

and the comparison threshold selected by this hierarchy is the 

SMCL-CA. The comparison thresholds used in this report are 

listed in tables 3A-K for all constituents and in tables 4-12 for 

constituents detected in groundwater samples from Tahoe–

Martis. One-hundred eight of the 240 constituents analyzed for 

this study have established thresholds. Detections of constituents at concentrations greater than the selected comparison 

thresholds are marked with asterisks in tables 4–12. 

Groundwater Quality Data

Results from analyses of raw (untreated) groundwater 

samples from Tahoe–Martis are presented in tables 4 through 

12. Groundwater samples collected in Tahoe–Martis were 

analyzed for up to 167 organic constituents, of which 156 

were not detected in any of the samples (tables 3A–E). The 

samples were analyzed for up to 71 naturally-occurring inorganic constituents and isotopic tracers (tables 3F–J) and two 

microbial constituents (table 3K). The results tables present 

only the constituents that were detected and list only samples 

in which at least one constituent was detected. The tables 

containing organic constituent classes that were analyzed 

at all of the grid wells include the number of wells at which 

each constituent was detected, the percentage of grid wells in 

which each constituent was detected, and the total number of 

constituents detected at each well (tables 5, 6). Results from 

the understanding wells are presented in the tables, but these 

results were excluded from the detection frequency calculations to avoid statistically over-representing the areas near the 

understanding wells.

Table 4 includes water-quality indicators measured in 

the field and at the NWQL, and tables 5 through 12 present 

the results of groundwater analyses organized by constituent 

classes: 

• Organic constituents

• VOCs and gasoline oxygenates and degradates 

(table 5)

• Pesticides and pesticide degradates (table 6)

• Inorganic constituents

• Nutrients (table 7)
12 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

• Major and minor ions and dissolved solids (table 8)

• Trace elements (table 9)

• Arsenic, iron, and chromium species (table 10)

• Isotopic tracers (table 11)

• Radioactive constituents (table 12A,B,C)

The constituents of special interest and the microbial constituents have no summary tables because none of these constituents were detected in groundwater samples from Tahoe–

Martis. Results for pharmaceutical compounds, and dissolved 

noble gases and tritium/helium age dates are not presented in 

this report; they will be included in subsequent publications.

Field Water-Quality Indicators

Field and laboratory measurements of dissolved oxygen, 

pH, specific conductance, alkalinity, and water temperature 

are given in table 4. Alkalinity and dissolved oxygen are used 

as indicators of natural processes that control water chemistry. 

Specific conductance is a measure of the electrical conductivity of water and is proportional to amount of total dissolved 

solids (TDS) in the water. Samples from 3 grid wells had field 

or laboratory specific-conductance values above the upper 

SMCL-CA, and specific-conductance values for samples from 

the other 38 wells were below the recommended SMCL-CA. 

The pH value indicates the acidity of the water. Low pH in 

water may contribute to corrosion and high pH in water may 

contribute to scaling. Samples from 10 grid wells had field 

pH values outside the SMCL-US range for pH (lower pH in 

7 samples and higher pH in 3 samples). Laboratory pH values 

may differ from field pH values because the pH of groundwater may change upon exposure to the atmosphere (see 

Appendix).

Organic Constituents

Volatile organic compounds (VOC) are present in paints, 

solvents, fuels, fuel additives, refrigerants, fumigants, and 

disinfected water, and are characterized by their tendency 

to evaporate. VOCs generally persist longer in groundwater 

than in surface water because groundwater is isolated from 

the atmosphere. Of the 88 VOCs analyzed, 8 were detected in 

groundwater samples; all detections except for one detection 

of perchloroethene (PCE) had concentrations below healthbased thresholds, and most had concentrations less than 1/100 

of the threshold values (table 5). Chloroform, a byproduct 

of drinking-water disinfection, and PCE, a solvent used in 

dry-cleaning, were detected in more than 10 percent of the 

grid well samples. These two compounds are among the most 

commonly detected VOCs in groundwater nationally (Zogorski and others, 2006). One or more VOCs were detected in 

samples from 15 of the 41 grid wells. 

Pesticides include herbicides, insecticides, and fungicides, and are used to control weeds, insects, fungi, and other 

pests in agricultural, urban, and suburban settings. Of the 63 

pesticides and pesticide degradates analyzed, 3 were detected 

in groundwater samples; all concentrations were below healthbased thresholds, and all were less than 1/100 of the threshold 

values (table 6). No compounds were detected in more than 10 

percent of the grid well samples. Pesticide compounds were 

detected in samples from 2 of the 41 grid wells.

Inorganic Constituents

Unlike the organic constituents and the constituents of 

special interest, most of the inorganic constituents are naturally present in groundwater, although their concentrations 

may be influenced by human activities.

Nutrients (nitrogen and phosphorus) in groundwater 

can affect biological activity in aquifers and in surface-water 

bodies that receive groundwater discharge. Nitrogen may be 

present in the form of ammonia, nitrite, or nitrate, depending on the oxidation-reduction state of the groundwater. High 

concentrations of nitrate can adversely affect human health, 

particularly the health of infants. All concentrations of nitrate, 

nitrite, and ammonia measured in samples from Tahoe–Martis 

wells were below health-based thresholds (table 7). 

 The major-ion composition, total dissolved solids (TDS) 

content, and levels of certain trace elements in groundwater 

can affect the aesthetic properties of water, such as taste, 

color, and odor, and the technical properties, such as scaling 

and staining. Although no adverse health effects are directly 

associated with these properties, they may reduce consumer 

satisfaction with the water or may have economic effects. 

CDPH has established nonenforceable thresholds (SMCL-CA) 

that are based on aesthetic or technical properties rather than 

health-based concerns for chloride and sulfate, TDS, iron, 

manganese, zinc, and silver.

Samples from 3 grid wells had TDS contents above the 

upper SMCL-CA, but TDS concentrations in samples from the 

other 38 grid wells were below the recommended SMCL-CA 

(table 8). The concentrations of chloride and sulfate were each 

above the upper SMCL-CA in one well, but concentrations 

were below the recommended SMCL-CA in all of the other 

grid wells. 

Iron and manganese are trace elements whose concentrations are affected by the oxidation-reduction state of the 

groundwater. Precipitation of minerals containing iron or manganese may cause orange, brown, or black staining of surfaces. 

Samples from 6 of the 41 grid wells had concentrations of iron 

and (or) manganese above the SMCL-CA (table 9). 
Water-Quality Results 13

Seventeen of the 24 trace elements analyzed in this study 

have regulatory or nonregulatory health-based thresholds. Of 

the 17 trace elements with health-based thresholds, all detections of 13 trace elements in grid wells had concentrations 

below health-based thresholds (table 9). Samples from 8 of the 

41 grid wells had arsenic concentrations above the MCL-US. 

Two of these samples also had boron concentrations above the 

NL-CA, and one of them had a strontium concentration above 

the HAL-US. Samples from two grid wells had concentrations 

of molybdenum above the HAL-US. 

Arsenic, iron, and chromium occur as different species, 

depending on the oxidation-reduction state of the groundwater. 

The oxidized and reduced species have different solubilities in 

groundwater and may have different effects on human health. 

The relative proportions of the oxidized and reduced species 

of each element can be used to help interpret the oxidation–

reduction state of the aquifer. Concentrations of total arsenic, 

total iron, and total chromium, and the concentrations of 

either the reduced or the oxidized species of each element are 

reported in table 10. The concentration of the other species can 

be calculated by the difference. The concentrations of arsenic, 

iron, and chromium reported in table 10 may be different than 

those reported in table 9 because different analytical methods 

were used (see Appendix). The concentrations reported in 

table 9 are considered to be more accurate.

Isotopic Tracers

Isotopic ratios of oxygen and hydrogen of water, strontium isotopic ratios, tritium and carbon-14 activities, and concentrations of dissolved noble gases may be used as tracers of 

natural processes affecting groundwater composition. Stable 

isotope ratios of hydrogen and oxygen of water (table 11) aid 

in interpretation of the sources of groundwater recharge. The 

stable isotope ratios of water reflect the altitude, latitude, and 

temperature of precipitation, and also the extent of evaporation 

of water from surface water bodies or soils prior to infiltration into the aquifer. Concentrations of dissolved noble gases 

are used to estimate the conditions of groundwater recharge, 

particularly the temperature of the recharge water. Noble gases 

dissolve in water that is in contact with the atmosphere, and 

the solubilities of the different noble gas species vary with 

temperature. Noble gas analyses were not completed in time 

to be included in this report; results will be presented in a subsequent publication. The isotopic ratio of strontium in groundwater reflects the strontium isotope ratio in the aquifer materials contributing strontium (and other inorganic constituents) 

to the groundwater. In regions with diverse geology, strontium 

isotope ratios may aid in estimating groundwater flow paths.

Tritium and carbon-14 activities (table 11), and helium 

isotope ratios provide information about the age (time since 

recharge) of the groundwater. Tritium is a short-lived radioactive isotope of hydrogen that is incorporated into the water 

molecule. Low levels of tritium are continuously produced 

by interaction of cosmic radiation with the Earth’s atmosphere, and a large amount of tritium was produced as a 

result atmospheric testing of nuclear weapons between 1952 

and 1963. Thus, concentrations of tritium above background 

generally indicate the presence of water recharged since the 

early 1950s. Helium isotope ratios are used in conjunction 

with tritium concentrations to estimate ages of young groundwater. Helium isotope ratio analyses were not completed in 

time to be included in this report; results will be presented in 

a subsequent publication. Carbon-14 is a radioactive isotope 

of carbon. Low levels of carbon-14 are continuously produced 

by interaction of cosmic radiation with the Earth’s atmosphere, and incorporated into atmospheric carbon dioxide. 

The carbon dioxide dissolves in precipitation, surface water, 

and groundwater exposed to the atmosphere, thereby entering the hydrologic cycle. Because carbon-14 has a half-life of 

approximately 5,700 years, low activities of carbon-14 relative 

to modern values generally indicate the presence of groundwater that is several thousand years old. 

Of the isotopic tracer constituents analyzed for this study, 

tritium is the only one that has a health-based threshold. All 

measured tritium activities in samples from Tahoe–Martis 

wells were less than 1/1,000 of the MCL-CA (table 11).

Radioactive Constituents

Radioactivity is the release of energy or energetic particles during changes in the structure of the nucleus of an atom. 

Most of the radioactivity in groundwater comes from decay of 

naturally-occurring isotopes of uranium and thorium that are 

present in minerals in the sediments or fractured rocks of the 

aquifer. Both uranium and thorium decay in a series of steps, 

eventually forming stable isotopes of lead (Soddy, 1913; Faure 

and Mensing, 2005). Radium-226, radium-228, and radon-222 

are radioactive isotopes formed during the uranium or thorium 

decay series. In each step in the decay series, one radioactive 

element turns into a different radioactive element by emitting an alpha or a beta particle from its nucleus. For example, 

radium-226 emits an alpha particle and therefore turns into 

radon-222. Radium-228 decays to form actinium-228 by 

emission of a beta particle. The alpha and beta particles emitted during radioactive decay are hazardous to human health 

because these energetic particles may damage cells. Radiation 

damage to cell DNA may increase the risk of getting cancer.

Activity is often used instead of concentration for 

reporting the presence of radioactive constituents. Activity of 

radioactive constituents in groundwater is measured in units of 

picocuries per liter (pCi/L), and one picocurie equals approximately two atoms decaying per minute. The number of atoms 

decaying is equal to the number of alpha or beta particles 

emitted. 
14 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

 Two MCL-USs have been proposed for radon-222. 

The higher, alternative MCL-US will apply if the State or 

local water agency has an approved multimedia mitigation 

program to address radon levels in indoor air (U.S. Environmental Protection Agency, 1999a). One of the 40 samples 

from grid wells analyzed for radon-222 had an activity above 

the alternative MCL-US (table 12A). Samples from 8 of the 

41 grid wells were analyzed for radium and gross alpha and 

gross beta particle activities. Two samples from grid wells 

had activities of gross alpha particle activity above the MCLUS (table 12B), and none had activities of radium above the 

MCL-US (table 12C).

Future Work

Subsequent reports will be focused on assessing the data 

presented in this report using a variety of statistical, qualitative, and quantitative approaches to evaluate the natural and 

human factors affecting groundwater quality. Water-quality 

data contained in the CDPH and the USGS NWIS databases, 

and water-quality data available from other State and local 

water agencies will be compiled, evaluated, and used in 

combination with the data that are presented in this report; 

the results of these future efforts will appear in one or more 

subsequent publications.

Summary 

Groundwater quality in the approximately 460-squaremile Tahoe–Martis study unit (Tahoe–Martis) was investigated 

in June through September 2007 as part of the Priority Basin 

Project of Groundwater Ambient Monitoring and Assessment 

(GAMA) Program. The California State Water Resources 

Control Board (SWRCB), in collaboration with the U.S. 

Geological Survey (USGS) and the Lawrence Livermore 

National Laboratory, is implementing the GAMA Program. 

The Priority Basin Project was designed by the USGS and the 

SWRCB in response to the State of California’s Groundwater 

Quality Monitoring Act of 2001. The project is a comprehensive assessment of statewide groundwater quality designed to 

identify and characterize risks to groundwater resources, and 

to increase the availability of information about groundwater 

quality to the public. Tahoe–Martis was the nineteenth study 

unit sampled as part of the project. 

Tahoe–Martis is in the northeast part of the Sierra 

Nevada hydrogeologic province and includes within it two 

groundwater basins defined by the California Department of 

Water Resources as wells as the watersheds surrounding these 

basins. The Tahoe–Martis study included an assessment of the 

groundwater quality in samples from 52 wells in El Dorado, 

Placer, and Nevada Counties. Forty-one of the wells were 

selected using a randomized grid approach to achieve a statistically unbiased representation of groundwater used for public 

drinking- water supplies. Eleven more wells were selected to 

provide additional sampling density to aid in understanding 

processes affecting groundwater quality. 

Groundwater samples were analyzed for VOCs, pesticides and pesticide degradates, pharmaceutical compounds, 

nutrients, major and minor ions, trace elements, radioactivity, and microbial constituents. Naturally occurring isotopes 

(stable isotopes of hydrogen and oxygen of water, isotopes of 

carbon, strontium, and uranium, and activities of tritium and 

carbon-14) and dissolved noble gases also were measured to 

provide a data set that will be used to help interpret the sources 

and ages of the sampled groundwater. In total, 240 constituents and field water-quality indicators were investigated for 

this study. This report describes the sampling, analytical, and 

quality-control methods used in the study, and presents the 

results of the chemical analyses made of the groundwater 

samples collected during June through September 2007.

This study did not attempt to evaluate the quality of water 

delivered to consumers; after withdrawal from the ground, 

water typically is treated, disinfected, and blended with 

other waters to maintain acceptable water quality. Regulatory thresholds apply to treated water that is served to the 

consumer, not to raw groundwater. However, to provide some 

context for the results, concentrations of constituents measured 

in the raw groundwater were compared with regulatory and 

nonregulatory health-based thresholds established by the U.S. 

Environmental Protection Agency (USEPA) and California 

Department of Public Health (CDPH) and thresholds established for aesthetic and technical concerns by CDPH.

The concentrations of most constituents detected in 

groundwater samples from Tahoe–Martis wells were below 

regulatory and nonregulatory drinking-water thresholds. One 

or more organic compounds (VOCs and/or pesticides) were 

detected in about 40 percent of the grid wells and generally at 

less than 1/100 of a regulatory or nonregulatory health-based 

threshold, although the perchloroethene concentration in 

one sample was above USEPA maximum contaminant level 

(MCL-US). Perchlorate, NDMA, and microbial constituents 

were not detected in samples from any wells. The concentrations of trace elements and nutrients were below regulatory 

or nonregulatory health-based thresholds with the following exceptions: Arsenic was detected above the MCL-US 

in samples from 20 percent of the grid wells. Gross alpha 

particle activity (MCL-US), boron (CDPH notification level), 

and molybdenum (USEPA lifetime health advisory) were 

each detected above thresholds in samples from two of the 

41 grid wells, and radon (proposed Alternative MCL-US) was 

detected above the threshold in a sample from one grid well. 

Fifteen percent of the samples from grid wells contained iron, 

manganese, or total dissolved solids at concentrations above 

the nonenforceable SMCL-CA thresholds set for aesthetic and 

technical concerns.

Subsequent reports will present evaluations of the data 

presented in this report using a variety of statistical, qualitative, and quantitative approaches to assess the natural and 

human factors affecting groundwater quality.
References Cited 15

Acknowledgments

The authors thank the following cooperators for their 

support: the California SWRCB, CDPH, CDWR, and LLNL. 

We especially thank the well owners and water purveyors for 

their generosity in allowing the USGS to collect samples from 

their wells. Two reviewers, Jan Stepek (SWRCB) and Carmen 

Burton (USGS) provided comments to improve this work. 

Funding for this work was provided by State bonds authorized 

by Proposition 50 and administered by the SWRCB.

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Tables 21

Tables
22 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table 1. Well identification, and sampling and construction information for wells sampled for the Tahoe–Martis Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June–September, 2007.—Continued

[GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; 

TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Other 

abbreviations: ft, foot; LSD, land surface datum; NAVD 88, North American Vertical Datum 1988; na, not available]

GAMA well 

identification 

number

Sampling information Construction information

Date Sampling 

schedule1

Elevation 

of LSD 

(ft above 

NAVD 88)2 

Well type

Well depth 

(ft below 

LSD)

Top of 

opening 

(ft below 

LSD)

Bottom 

of opening 

(ft below 

LSD)

Grid wells

TMART-01 06/25/07 Slow 5,847 Production 1,132 280 1,110

TMART-02 06/26/07 Intermediate 6,125 Production 690 65 680

TMART-03 06/26/07 Intermediate 5,596 Production 383 363 383

TMART-04 06/27/07 Intermediate 5,889 Production 1,026 100 1,026

TMART-05 06/27/07 Intermediate 5,968 Production 1,370 460 1,360

TMART-06 06/28/07 Slow 5,879 Production 900 40 900

TMART-07 07/10/07 Intermediate 5,884 Production 106 50 na

TMART-08 07/10/07 Intermediate 5,973 Production 612 125 612

TMART-09 09/20/07 Intermediate 5,940 Production 120 70 120

TMART-10 07/16/07 Intermediate 6,604 Production 600 500 600

TMART-11 07/18/07 Intermediate 5,914 Production 132 na na

TMART-12 07/26/07 Intermediate 5,871 Production 250 175 250

TMART-13 09/11/07 Intermediate 5,857 Production 175 175 na

TMART-14 09/12/07 Intermediate 5,840 Production 800 217 800

TROCK-01 07/9/07 Intermediate 6,044 Production 270 na na

TROCK-02 07/11/07 Intermediate 6,584 Spring 0 na na

TROCK-03 07/16/07 Intermediate 6,064 Production 292 232 292

TROCK-04 07/17/07 Intermediate 7,209 Spring 0 na na

TROCK-05 07/17/07 Intermediate 6,758 Spring 0 na na

TROCK-06 07/18/07 Intermediate 6,314 Production 218 75 213

TROCK-07 07/24/07 Intermediate 6,319 Production 320 190 320

TROCK-08 07/30/07 Intermediate 8,107 Spring 0 na na

TROCK-09 07/30/07 Intermediate 7,615 Spring 0 na na

TROCK-10 07/31/07 Intermediate 6,316 Production 610 na na

TROCK-11 08/01/07 Intermediate 6,354 Production 48 na na

TROCK-12 09/12/07 Intermediate 6,056 Production na na na

TROCK-13 09/13/07 Slow 5,984 Production 102 93 98

TTAHO-01 07/11/07 Intermediate 6,232 Production 50 45 50

TTAHO-02 07/19/07 Slow 6,443 Production 880 240 880

TTAHO-03 07/23/07 Intermediate 6,293 Production 152 124 144

TTAHO-04 07/24/07 Intermediate 6,405 Production 240 60 210

TTAHO-05 07/25/07 Intermediate 6,400 Production 482 228 452

TTAHO-06 08/02/07 Slow 6,232 Production 495 138 480

TTAHO-07 08/13/07 Intermediate 6,309 Production 266 108 160

TTAHO-08 08/14/07 Intermediate 6,254 Production 156 86 156

TTAHO-09 08/15/07 Intermediate 6,214 Production 100 70 100

TTAHO-10 08/16/07 Slow 6,319 Production 250 95 245

TTAHO-11 08/21/07 Slow 6,472 Monitoring 200 na na

TTAHO-12 08/22/07 Intermediate 6,304 Monitoring 325 106 315

TTAHO-13 08/29/07 Slow 6,281 Monitoring 135 130 135

TTAHO-14 09/10/07 Intermediate 6,241 Production 250 135 245

Table 1. Well identification, and sampling and construction information for wells sampled for the Tahoe–Martis Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June–September, 2007.

[GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; 

TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Other 

abbreviations: ft, foot; LSD, land surface datum; NAVD 88, North American Vertical Datum 1988; na, not available]
Tables 23

Table 1. Well identification, and sampling and construction information for wells sampled for the Tahoe–Martis Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June–September, 2007.—Continued

[GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; 

TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Other 

abbreviations: ft, foot; LSD, land surface datum; NAVD 88, North American Vertical Datum 1988; na, not available]

GAMA well 

identification 

number

Sampling information Construction information

Date Sampling 

schedule1

Elevation 

of LSD 

(ft above 

NAVD 88)2 

Well type

Well depth 

(ft below 

LSD)

Top of 

opening 

(ft below 

LSD)

Bottom 

of opening 

(ft below 

LSD)

Understanding Wells

TMARTU-01 07/12/07 Slow 5,996 Production 900 140 900

TROCKU-01 07/09/07 Intermediate 6,984 Production 317 285 317

TROCKU-02 07/25/07 Intermediate 6,645 Production 860 380 800

TTAHOU-01 08/13/07 Intermediate 6,304 Production 330 130 310

TTAHOU-02 08/14/07 Intermediate 6,259 Production 418 110 400

TTAHOU-03 08/14/07 Intermediate 6,284 Production 380 186 366

TTAHOU-04 3

08/23/07 Intermediate 6,263 Production 247 152 220

TTAHOU-05 08/27/07 Slow 6,281 Monitoring 335 325 335

TTAHOU-06 08/28/07 Intermediate 6,281 Monitoring 255 245 255

TTAHOU-07 08/28/07 Intermediate 6,281 Monitoring 163 158 163

TTAHOU-08 09/10/07 Intermediate 6,281 Monitoring 93 88 93

1

Sampling schedules are described in table 2.

2

Land-surface datum (LSD) is a datum plane that is approximately at land surface at each well. The elevation of the LSD is described in feet above the North 

American Vertical Datum 1988.

3

Well was sampled for volatile organic compounds (VOC) on 04/03/08.
24 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Analyte classes Slow 

schedule

Intermediate 

schedule

Analyte 

list table

Results 

table

Water-quality indicators

Dissolved oxygen, temperature, specific conductance X X — 4

pH, alkalinity X X — 4

Organic constituents

Volatile organic compounds X X 3A 5

Gasoline additives and oxygenates1 X X 3B 5

Pesticides and pesticide degradates X X 3C 6

Pharmaceutical compounds X — 3D (2)

Constituents of special interest

Perchlorate X X 3E (3)

N-Nitrosodimethylamine (NDMA) X — 3E (3)

Inorganic constituents

Nutrients X X 3F 7

Major and minor ions and total dissolved solids X X 3G 8

Trace elements X X 3G 9

Arsenic, iron, and chromium species X X 3H 10

Isotopic tracers

Stable isotopes of hydrogen and oxygen of water X X 3I 11

Stable isotopes of carbon and carbon-14 activity X X 3I 11

Strontium isotope ratio X X 3I 11

Radioactivity and noble gases

Tritium X X 3I 11

Tritium and noble gases X X 3J (2)

Radium isotopes X — 3I 12

Radon-222 X X 3I 12

Uranium isotopes X X 3I 12

Gross alpha and beta radiation X — 3I 12

Microbial constituents

Viral indicators X — 3K (3)

Table 2. Classes of chemical and microbial constituents and water-quality indicators collected for the slow and intermediate sampling 

schedules for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September, 2007.

[X, analyte class collected; —, analyte class not collected or no table]

1

Collected in the Tahoe study area only.

2

Data will be presented in subsequent reports

3

Constituents were not detected in any samples.
Tables 25

Table 3A. Volatile organic compounds and gasoline additives, primary uses or sources, comparative thresholds, and reporting information 

for the U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2020.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of 

June 1, 2008. Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, 

California Department of Public Health notification level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk 

factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; THM, trihalomethane; D, detected in 

groundwater samples (table 5); na, not available; μg/L, microgram per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS number1 LRL 

(μg/L)

Threshold 

type2

Threshold 

value 

(μg/L)

Detection

Acetone Solvent 81552 67-64-1 6 na na —

Acrylonitrile Organic synthesis 34215 107-13-1 0.4 RSD5-US 0.6 —

tert-Amyl methyl ether (TAME) Gasoline oxygenate 50005 994-05-8 0.04 na na —

Benzene Gasoline hydrocarbon 34030 71-43-2 0.016 MCL-CA 1 —

Bromobenzene Solvent 81555 108-86-1 0.02 na na —

Bromochloromethane Fire retardant 77297 74-97-5 0.06 HAL-US 90 —

Bromodichloromethane Disinfection by-product 

(THM)

32101 75-27-4 0.04 MCL-US 3

80 D

Bromoform (tribromomethane) Disinfection by-product 

(THM)

32104 75-25-2 0.08 MCL-US 3

80 —

Bromomethane (methyl bromide)Fumigant 34413 74-83-9 0.4 HAL-US 10 —

n-Butylbenzene Gasoline hydrocarbon 77342 104-51-8 0.14 NL-CA 260 —

sec-Butylbenzene Gasoline hydrocarbon 77350 135-98-8 0.04 NL-CA 260 —

tert-Butylbenzene Gasoline hydrocarbon 77353 98-06-6 0.08 NL-CA 260 —

Carbon disulfide Organic synthesis, natural 77041 75-15-0 0.06 NL-CA 160 D

Carbon tetrachloride (tetrachloromethane)Solvent 32102 56-23-5 0.08 MCL-CA 0.5 —

Chlorobenzene Solvent 34301 108-90-7 0.02 MCL-CA 70 —

Chloroethane Solvent 34311 75-00-3 0.10 na na —

Chloroform (trichloromethane) Disinfection by-product 

(THM)

32106 67-66-3 0.04 MCL-US 3

80 D

Chloromethane Solvent 34418 74-87-3 0.10 HAL-US 30 —

3-Chloropropene Organic synthesis 78109 107-05-1 0.08 na na —

2-Chlorotoluene Solvent 77275 95-49-8 0.04 NL-CA 140 —

4-Chlorotoluene Solvent 77277 106-43-4 0.04 NL-CA 140 —

Dibromochloromethane Disinfection by-product 

(THM)

32105 124-48-1 0.12 MCL-US 3

80 —

1,2-Dibromo-3-chloropropane 

(DBCP)

Fumigant 82625 96-12-8 0.5 MCL-US 0.2 —

1,2-Dibromoethane (EDB) Fumigant 77651 106-93-4 0.04 MCL-US 0.05 —

Dibromomethane Solvent 30217 74-95-3 0.04 na na —

1,2-Dichlorobenzene Solvent 34536 95-50-1 0.04 MCL-CA 600 —

1,3-Dichlorobenzene Solvent 34566 541-73-1 0.04 HAL-US 600 —

1,4-Dichlorobenzene Fumigant 34571 106-46-7 0.04 MCL-CA 5 —

trans-1,4-Dichloro-2-butene Organic synthesis 73547 110-57-6 0.6 na na —

Dichlorodifluoromethane (CFC12)Refrigerant 34668 75-71-8 0.14 NL-CA 1,000 — 

1,1-Dichloroethane (1,1-DCA) Solvent 34496 75-34-3 0.06 MCL-CA 5 —

1,2-Dichloroethane (1,2-DCA) Solvent 32103 107-06-2 0.10 MCL-CA 0.5 —

1,1-Dichloroethene (1,1-DCE) Organic synthesis 34501 75-35-4 0.02 MCL-CA 6 —

cis-1,2-Dichloroethene (cis-1,2-

DCE)

Solvent 77093 156-59-2 0.02 MCL-CA 6 —

trans-1,2-Dichloroethene (trans1,2-DCE)

Solvent 34546 156-60-5 0.018 MCL-CA 10 —

1,2-Dichloropropane Fumigant 34541 78-87-5 0.02 MCL-US 5 —

1,3-Dichloropropane Fumigant 77173 142-28-9 0.06 na na —

2,2-Dichloropropane Fumigant 77170 594-20-7 0.06 na na —

1,1-Dichloropropene Organic synthesis 77168 563-58-6 0.04 na na —

Table 3A. Volatile organic compounds and gasoline additives, primary uses or sources, comparative thresholds, and reporting 

information for the U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2020.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of June 1, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification 

level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, 

laboratory reporting level; THM, trihalomethane; D, detected in groundwater samples (table 5); na, not available; μg/L, microgram per liter; —, not detected]
26 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table 3A. Volatile organic compounds and gasoline additives, primary uses or sources, comparative thresholds, and reporting information 

for the U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2020.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of 

June 1, 2008. Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, 

California Department of Public Health notification level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk 

factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; THM, trihalomethane; D, detected in 

groundwater samples (table 5); na, not available; μg/L, microgram per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS number1 LRL 

(μg/L)

Threshold 

type2

Threshold 

value 

(μg/L)

Detection

cis-1,3-Dichloropropene Fumigant 34704 10061-01-5 0.06 RSD5-US 4

4 —

trans-1,3-Dichloropropene Fumigant 34699 10061-02-6 0.10 RSD5-US 4

4 —

Diethyl ether Solvent 81576 60-29-7 0.08 na na —

Diisopropyl ether (DIPE) Gasoline oxygenate 81577 108-20-3 0.06 na na D

Ethylbenzene Gasoline hydrocarbon 34371 100-41-4 0.02 MCL-CA 300 —

Ethyl tert-butyl ether (ETBE) Gasoline oxygenate 50004 637-92-3 0.04 na na —

Ethyl methacrylate Organic synthesis 73570 97-63-2 0.14 na na —

o-Ethyl toluene (1-ethyl-2-

methyl benzene)

Gasoline hydrocarbon 77220 611-14-3 0.04 na na —

Hexachlorobutadiene Organic synthesis 39702 87-68-3 0.10 RSD5-US 9 —

Hexachloroethane Solvent 34396 67-72-1 0.14 HAL-US 1 —

2-Hexanone (n-Butyl methyl 

ketone)

Solvent 77103 591-78-6 0.4 na na —

Iodomethane (Methyl iodide) Organic synthesis 77424 74-88-4 0.4 na na —

Isopropylbenzene Gasoline hydrocarbon 77223 98-82-8 0.04 NL-CA 770 —

4-Isopropyl-1-methyl benzene Gasoline hydrocarbon 77356 99-87-6 0.08 na na —

Methyl acrylate Organic synthesis 49991 96-33-3 0.4 na na —

Methyl acrylonitrile Organic synthesis 81593 126-98-7 0.4 na na —

Methyl tert-butyl ether (MTBE) Gasoline oxygenate 78032 1634-04-4 0.10 MCL-CA 13 D

Methyl iso-butyl ketone 

(MIBK)

Solvent 78133 108-10-1 0.2 NL-CA 120 —

Methylene chloride (dichloromethane)Solvent 34423 75-09-2 0.04 MCL-US 5 — 

Methyl ethyl ketone (2-butanone, MEK)Solvent 81595 78-93-3 1.6 HAL-US 4,000 —

Methyl methacrylate Organic synthesis 81597 80-62-6 0.20 na na —

Naphthalene Gasoline hydrocarbon 34696 91-20-3 0.4 NL-CA 17 —

Perchloroethene (tetrachloroethene, PCE)Solvent 34475 127-18-4 0.04 MCL-US 5 D

n-Propylbenzene Solvent 77224 103-65-1 0.04 NL-CA 260 —

Styrene Gasoline hydrocarbon 77128 100-42-5 0.04 MCL-US 100 —

1,1,1,2-Tetrachloroethane Solvent 77562 630-20-6 0.04 HAL-US 70 —

1,1,2,2-Tetrachloroethane Solvent 34516 79-34-5 0.10 MCL-CA 1 —

Tetrahydrofuran Solvent 81607 109-99-9 1.0 na na — 5

1,2,3,4-Tetramethylbenzene Gasoline hydrocarbon 49999 488-23-3 0.14 na na — 

1,2,3,5-Tetramethylbenzene Gasoline hydrocarbon 50000 527-53-7 0.12 na na — 

Toluene Gasoline hydrocarbon 34010 108-88-3 0.018 MCL-CA 150 — 5

1,2,3-Trichlorobenzene Organic synthesis 77613 87-61-6 0.12 na na — 

1,2,4-Trichlorobenzene Solvent 34551 120-82-1 0.12 MCL-CA 5 —

1,1,1-Trichloroethane 

(1,1,1-TCA)

Solvent 34506 71-55-6 0.04 MCL-CA 200 D

1,1,2-Trichloroethane Solvent 34511 79-00-5 0.04 MCL-CA 5 —

Trichloroethene (TCE) Solvent 39180 79-01-6 0.02 MCL-US 5 D

Trichlorofluoromethane 

(CFC-11)

Refrigerant 34488 75-69-4 0.08 MCL-CA 150 —
Tables 27

Table 3A. Volatile organic compounds and gasoline additives, primary uses or sources, comparative thresholds, and reporting information 

for the U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2020.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of 

June 1, 2008. Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, 

California Department of Public Health notification level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk 

factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; THM, trihalomethane; D, detected in 

groundwater samples (table 5); na, not available; μg/L, microgram per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS number1 LRL 

(μg/L)

Threshold 

type2

Threshold 

value 

(μg/L)

Detection

1,2,3-Trichloropropane (1,2,3-

TCP)

Solvent/organic synthesis 77443 96-18-4 0.12 HAL-US6 40 —

Trichlorotrifluoroethane (CFC113)Refrigerant 77652 76-13-1 0.04 MCL-CA 1,200 —

1,2,3-Trimethylbenzene Gasoline hydrocarbon 77221 526-73-8 0.08 na na —

1,2,4-Trimethylbenzene Gasoline hydrocarbon 77222 95-63-6 0.04 NL-CA 330 — 5

1,3,5-Trimethylbenzene Organic synthesis 77226 108-67-8 0.04 NL-CA 330 —

Vinyl bromide (bromoethene) Fire retardant 50002 593-60-2 0.12 na na —

Vinyl chloride (chloroethene) Organic synthesis 39175 75-01-4 0.08 MCL-CA 0.5 —

m- and p-Xylene Gasoline hydrocarbon 85795 108-38-3/

106-42-3

0.08 MCL-CA 7

1,750 —

o-Xylene Gasoline hydrocarbon 77135 95-47-6 0.04 MCL-CA 7

1,750 —

1

This report contains CAS Registry Numbers®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the 

CASRNs through CAS Client ServicesSM.

2

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

3

The MCL-US threshold for trihalomethanes is the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.

4

The RSD5 threshold for 1,3-dichloropropene is the sum of its isomers (cis and trans).

5

All detections of tetrahydrofuran, toluene, and 1,2,4-trimethylbenzene were V-coded because of detections in field blanks and were excluded from the dataset 

of groundwater quality results.

6

In earlier reports in this series, the NL-CA (0.005 μg/L) was used as the comparison threshold for 1,2,3-TCP.

7

The MCL-CA threshold for m- and p-Xylene and o-Xylene is the sum all three xylene compounds.
28 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Constituent Primary use 

or source

USGS 

parameter 

code

CAS number LRL 

(μg/L)

Threshold 

type1

Threshold 

value 

(μg/L)

Detection

Acetone Degradate 81552 67-64-1 1.2 na na —

tert-Amyl alcohol Oxygenate 77073 75-85-4 0.6 na na —

tert-Amyl methyl ether (TAME) Oxygenate 50005 994-05-8 0.05 na na —

tert-Butyl alcohol (TBA) Degradate 77035 75-65-0 2 NL-CA 12 —

Diisopropyl ether (DIPE) Oxygenate 81577 108-20-3 0.06 na na D

Ethyl tert-butyl ether (ETBE) Oxygenate 50004 637-92-3 0.04 na na —

Methyl acetate Degradate 77032 79-20-9 0.4 na na —

Methyl tert-butyl ether (MTBE) Oxygenate 78032 1634-04-4 0.04 MCL-CA 13 D

 1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 

Table 3B. Gasoline oxygenates and degradates, primary uses or sources, comparative thresholds, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 4024.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level. 

Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples (table 5); na, not available; μg/L, 

microgram per liter; —, not detected]
Tables 29

Table 3C. Pesticides and pesticide degradates, primary uses or sources, comparative thresholds, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2003.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of June 1, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples 

(table 6); na, not available; μg/L, microgram per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS number LRL 

(μg/L)

Threshold 

type1

Threshold 

value 

(μg/L)

Detection

Acetochlor Herbicide 49260 34256-82-1 0.006 na na —

Alachlor Herbicide 46342 15972-60-8 0.005 MCL-US 2 —

Atrazine Herbicide 39632 1912-24-9 0.007 MCL-CA 1 D

Azinphos-methyl Insecticide 82686 86-50-0 0.08 na na —

Azinphos-methyl-oxon Insecticide degradate 61635 961-22-8 0.042 na na —2

Benfluralin Herbicide 82673 1861-40-1 0.01 na na —2

Carbaryl Insecticide 82680 63-25-2 0.06 RSD5-US 400 —

2-Chloro-2,6-

diethylacetanilide 

Herbicide degradate 61618 6967-29-9 0.0065 na na —

4-Chloro-2-methylphenol Herbicide degradate 61633 1570-64-5 0.005 na na —

Chlorpyrifos Insecticide 38933 2921-88-2 0.005 HAL-US 2 —

Chlorpyrifos oxon Insecticide degradate 61636 5598-15-2 0.0562 na na —2

Cyfluthrin Insecticide 61585 68359-37-5 0.053 na na —

Cypermethrin Insecticide 61586 52315-07-8 0.046 na na —

Dacthal (DCPA) Herbicide 82682 1861-32-1 0.003 HAL-US 70 —

Deethylatrazine (2-chloro-4-

isopropylamino-6-amino-striazine)

Herbicide degradate 04040 6190-65-4 0.014 na na D2

Desulfinylfipronil Insecticide degradate 62170 na 0.012 na na —

Desulfinylfipronil amide Insecticide degradate 62169 na 0.029 na na —

Diazinon Insecticide 39572 333-41-5 0.005 HAL-US 1 —

3,4-Dichloroaniline Herbicide degradate 61625 95-76-1 0.0045 na na —

Dichlorvos Insecticide 38775 62-73-7 0.013 na na —2

Dicrotophos Insecticide 38454 141-66-2 0.0843 na na D2

Dieldrin Insecticide 39381 60-57-1 0.009 RSD5-US 0.02 —

2,6-Diethylaniline Herbicide degradate 82660 579-66-8 0.006 na na —

Dimethoate Insecticide 82662 60-51-5 0.0061 na na —2

Ethion Insecticide 82346 563-12-2 0.016 na na —

Ethion monoxon Insecticide degradate 61644 17356-42-2 0.021 na na —

2-Ethyl-6-methylaniline Herbicide degradate 61620 24549-06-2 0.01 na na —

Fenamiphos Insecticide 61591 22224-92-6 0.03 HAL-US 0.7 —

Fenamiphos sulfone Insecticide degradate 61645 31972-44-8 0.053 na na —

Fenamiphos sulfoxide Insecticide degradate 61646 31972-43-7 0.04 na na —2

Fipronil Insecticide 62166 120068-37-3 0.016 na na —

Fipronil sulfide Insecticide degradate 62167 120067-83-6 0.013 na na —

Fipronil sulfone Insecticide degradate 62168 120068-36-2 0.024 na na —

Fonofos Insecticide 04095 944-22-9 0.006 HAL-US 10 —

Hexazinone Herbicide 04025 51235-04-2 0.026 HAL-US 400 —

Iprodione Fungicide 61593 36734-19-7 0.026 na na —

Isofenphos Insecticide 61594 25311-71-1 0.011 na na —

Table 3C. Pesticides and pesticide degradates, primary uses or sources, comparative thresholds, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2003.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of June 1, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples 

(table 6); na, not available; μg/L, microgram per liter; —, not detected]
30 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table 3C. Pesticides and pesticide degradates, primary uses or sources, comparative thresholds, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2003.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of June 1, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples 

(table 6); na, not available; μg/L, microgram per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS number LRL 

(μg/L)

Threshold 

type1

Threshold 

value 

(μg/L)

Detection

Malaoxon Insecticide degradate 61652 1634-78-2 0.039 na na —

Malathion Insecticide 39532 121-75-5 0.016 HAL-US 100 —

Metalaxyl Fungicide 61596 57837-19-1 0.0069 na na —

Methidathion Insecticide 61598 950-37-8 0.0087 na na —

Metolachlor Herbicide 39415 51218-45-2 0.01 HAL-US 700 —

Metribuzin Herbicide 82630 21087-64-9 0.012 HAL-US 70 —

Myclobutanil Fungicide 61599 88671-89-0 0.033 na na —

1-Naphthol Insecticide degradate 49295 90-15-3 0.0882 na na —2

Paraoxon-methyl Insecticide degradate 61664 950-35-6 0.019 na na —

Parathion-methyl Insecticide 82667 298-00-0 0.008 HAL-US 1 —

Pendimethalin Herbicide 82683 40487-42-1 0.02 na na —

cis-Permethrin Insecticide 82687 54774-45-7 0.01 na na —

Phorate Insecticide 82664 298-02-2 0.02 na na —2

Phorate oxon Insecticide degradate 61666 2600-69-3 0.027 na na —

Phosmet Insecticide 61601 732-11-6 0.0079 na na —2

Phosmet oxon Insecticide degradate 61668 3735-33-9 0.0511 na na —2

Prometon Herbicide 04037 1610-18-0 0.01 HAL-US 100 —

Prometryn Herbicide 04036 7287-19-6 0.0059 na na —

Pronamide (propyzamide) Herbicide 82676 23950-58-5 0.004 RSD5-US 20 —

Simazine Herbicide 04035 122-34-9 0.006 MCL-US 4 —

Tebuthiuron Herbicide 82670 34014-18-1 0.016 HAL-US 500 —

Terbufos Insecticide 82675 13071-79-9 0.012 HAL-US 0.4 —

Terbufos oxon sulfone Insecticide degradate 61674 56070-15-6 0.045 na na —

Terbuthylazine Herbicide 04022 5915-41-3 0.0083 na na —

Tribufos Defoliant 61610 78-48-8 0.035 na na —

Trifluralin Herbicide 82661 1582-09-8 0.009 HAL-US 10 — 1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

The median matrix-spike recovery was less than 70 percent. Low recoveries may indicate that the compound might not have been detected in some samples 

if it was present at very low concentrations.
Tables 31

Constituent Primary use 

or source

USGS 

parameter 

code

CAS number SRL1

(μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Acetaminophen Analgesic 62000 103-90-2 0.180 na na

Albuterol Bronchodilator 62020 18559-94-9 0.025 na na

Caffeine Stimulant 50305 58-08-2 0.080 na na

Carbamazapine Anticonvulsant; mood stabilizer 62793 298-46-4 0.023 na na

Codeine Opiod narcotic 62003 76-57-3 0.018 na na

Cotinine Nicotine metabolite 62005 486-56-6 0.013 na na

Dehydronifedipine Antianginal metabolite 62004 67035-22-7 0.033 na na

Diltiazem Antianginal; antihypertensive 62008 42399-41-7 0.021 na na

1,7-Dimethylxanthine Caffeine metabolite 62030 611-59-6 0.054 na na

Diphenhydramine Antihistamine 62796 58-73-1 0.018 na na

Sulfamethoxazole Antibiotic 62021 723-46-6 0.046 na na

Thiabendazole Anthelmintic 62801 148-79-8 0.021 na na

Trimethoprim Antibiotic 62023 738-70-5 0.013 na na

Warfarin Anticoagulant 62024 81-81-2 0.030 na na

1

The California Groundwater Ambient Monitoring and Assessment (GAMA) program uses reporting limits for the pharmaceutical compounds that are more 

conservative than those used by the USGS National Water Quality Laboratory (NWQL). The data for samples from this study unit were reported by the NWQL 

with interim laboratory reporting limits, and results below the interim method detection limits were included in the dataset. The GAMA program examined 

laboratory quality-control data and decided that the rate of false-positive detections was too high using the interim laboratory reporting limits. On the basis of 

our independent evaluation of the laboratory quality-control data, the GAMA program defined study reporting limits (SRL) for the pharmaceutical compounds. 

These SRLs have significantly higher concentrations than the interim laboratory reporting limits originally reported with the data, and GAMA does not report 

results below the SRLs. For albuterol, carbamazepine, codeine, cotinine, dehydronifedipine, diltiazem, 1,7-dimethylxanthine, sulfamethoxazole, thiabendazole, 

trimethoprim, and warfarin, the SRLs correspond to the long-term method detection limits determined by the USGS Branch of Quality Systems in October 2007 

(LT-MDL). For acetaminophen, caffeine, and diphenhydramine, the SRLs correspond to the concentration above which there is less than a 1 percent probability 

of a false-positive detection determined from assessing laboratory quality-control data and field blanks associated with GAMA samples collected from May 

2004 through September 2007. The SRLs for those compounds are higher than the BQS LT-MDLs. Detections reported by the USGS National Water Quality 

Laboratory with concentrations lower than the GAMA SRL are reported as non-detections by the GAMA program.

Table 3D. Pharmaceutical compounds, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey (USGS) National Water Quality Laboratory schedule 2080.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of June 1, 2008. 

Abbreviations: CAS, Chemical Abstract Service; na, not available; SRL, study reporting limit; μg/L, microgram per liter; —, not detected]
32 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table 3E. Constituents of special interest, primary uses or sources, comparative thresholds, and reporting information for the 

Montgomery Watson Harza and Weck Laboratories.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; NL-CA, California Department of Public Health notification level. 

Laboratories: MWH: Montgomery Watson Harza Laboratory; Weck, Weck Laboratory. Other abbreviations: CAS, Chemical Abstract Service; MRL, minimum 

reporting level; μg/L, microgram per liter; —, not detected]

Constituent Primary use or source

USGS 

parameter 

code

CAS number

MWH 

MRL 

(μg/L)

 Weck 

MRL 

(μg/L)

Threshold 

type1

Threshold 

value 

(μg/L)

Detection

Perchlorate2 Rocket fuel, fireworks, 

natural

61209 14797-73-0 0.5 0.1 MCL-CA 6 —

N-Nitrosodimethylamine (NDMA)3

Rocket fuel, plasticizer, disinfection 

byproduct

64176 62-75-9 0.002 0.002 NL-CA 0.010 —

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

All 52 samples were analyzed for perchlorate by MWH, and 15 samples collected after August 20, 2008, were also analyzed by Weck.

3

All 10 samples on the slow schedule were analyzed for NDMA by MHW, and 3 samples on the slow schedule collected after August 20, 2008, were also 

analyzed by Weck.

Constituent

USGS 

parameter 

code

CAS number LRL 

(mg/L)

Threshold 

type1

Threshold 

value 

(mg/L)

Detection

Ammonia, as nitrogen 00608 7664-41-7 0.010 HAL-US 2

24.7 D

Nitrite, as nitrogen 00613 14797-65-0 0.002 MCL-US 1 D

Nitrite plus nitrate, as nitrogen 00631 na 0.060 MCL-US 10 D

Total nitrogen (ammonia, nitrite, nitrate, organic 

nitrogen)

62854 17778-88-0 0.06 na na D

Orthophosphate, as phosphorus 00671 14265-44-2 0.006 na na D

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

The HAL-US is 30 mg/L "as ammonia." To facilitate comparson to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L "as 

nitrogen."

Table 3F. Nutrients and dissolved organic carbon, comparative thresholds, and reporting information for the U.S. Geological Survey 

(USGS) National Water Quality Laboratory Schedule 2755.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of June 1, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples (table 7); na, 

not available; mg/L, milligram per liter]
Tables 33

Constituent

USGS 

parameter 

code

CAS number LRL Threshold 

type1

Threshold 

value Detection

Major and minor ions (mg/L)

Bromide 71870 24959-67-9 0.02 na na D

Calcium 00915 7440-70-2 0.02 na na D

Chloride 00940 16887-00-6 0.12 SMCL-CA 2

250 (500) D

Fluoride 00950 16984-48-8 0.10 MCL-CA 2 D

Iodide 71865 7553-56-2 0.002 na na D

Magnesium 00925 7439-95-4 0.014 na na D

Potassium 00935 7440-09-7 0.04 na na D

Silica 00955 7631-86-9 0.018 na na D

Sodium 00930 7440-23-5 0.20 na na D

Sulfate 00945 14808-79-8 0.18 SMCL-CA 2

250 (500) D

Residue on evaporation (total dissolved 

solids, TDS)

70300 na 10 SMCL-US 2

500 

(1,000)

D

Trace elements (μg/L)

Aluminum 01106 7429-90-5 1.6 MCL-CA 1,000 D

Antimony 01095 7440-36-0 0.06 MCL-US 6 D

Arsenic 01000 7440-38-2 0.12 MCL-US 10 D

Barium 01005 7440-39-3 0.08 MCL-CA 1,000 D

Beryllium 01010 7440-41-7 0.06 MCL-US 4 D

Boron 01020 7440-42-8 8 NL-CA 1,000 D

Cadmium 01025 7440-43-9 0.04 MCL-US 5 D

Chromium 01030 7440-47-3 0.12 MCL-CA 50 D

Cobalt 01035 7440-48-4 0.04 na na D

Copper 01040 7440-50-8 0.4 AL-US 1,300 D

Iron 01046 7439-89-6 6 SMCL-CA 300 D

Lead 01049 7439-92-1 0.12 AL-US 15 D

Lithium 01130 7439-93-2 0.6 na na D

Manganese 01056 7439-96-5 0.2 SMCL-CA 50 D

Molybdenum 01060 7439-98-7 0.12 HAL-US 40 D

Nickel 01065 7440-02-0 0.06 MCL-CA 100 D

Selenium 01145 7782-49-2 0.08 MCL-US 50 D

Silver 01075 7440-22-4 0.10 SMCL-CA 100 —

Strontium 01080 7440-24-6 0.4 HAL-US 4,000 D

Thallium 01057 7440-28-0 0.04 MCL-US 2 D

Tungsten 01155 7440-33-7 0.06 na na D

Uranium 22703 7440-61-1 0.04 MCL-US 30 D

Vanadium 01085 7440-62-2 0.04 NL-CA 50 D

Zinc 01090 7440-66-6 0.6 SMCL-CA 5,000 D

Table 3G. Major and minor ions and trace elements, comparative thresholds, and reporting information for the U.S. Geological Survey 

(USGS) National Water Quality Laboratory Schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of June 1, 2008. 

Threshold type: AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; 

MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; 

NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. 

Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples (tables 8, 9); na, not available; 

mg/L, milligram per liter; μg/L, microgram per liter; —, not detected]

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

The recommended SMCL-CA thresholds for chloride, sulfate, and TDS are listed with the upper SMCL-CA thresholds in parentheses.
34 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Constituent 

(valence state)

USGS 

parameter 

code

CAS number MDL 

(μg/L)

Threshold 

type1

Threshold 

level 

(μg/L)

Detection

Arsenic(III) 99034 22569-72-8 1 na na D

Arsenic(total) 99033 7440-38-2 0.5 MCL-US 10 D

Chromium(VI) 01032 18540-29-9 1 na na D

Chromium(total) 01030 7440-47-3 1 MCL-CA 50 D

Iron(II) 01047 7439-89-6 2 na na D

Iron(total) 01046 7439-89-6 2 SMCL-CA 300 D

Table 3H. Arsenic, chromium, and iron species, comparative thresholds, and reporting information for the U.S. Geological Survey 

(USGS) Trace Metal Laboratory, Boulder, Colorado.

[The five-digit USGS parameter code is used to uniquely identify a specific constituents or property. Thresholds and threshold values as of June 1, 2008. 

Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: CAS, Chemical Abstract 

Service; MDL, method detection limit; na, not available; μg/L, microgram per liter; D, detected in groundwater samples (table 10)]

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.
Tables 35

Constituent

USGS 

parameter 

code

CAS number

Reporting 

level 

type

Reporting 

level or 

 uncertainty

Threshold 

type1

Threshold 

value Detection

Stable isotope ratios (per mil)

δ2H of water2 82082 na MU 2 na na D

δ18O of water2 82085 na MU 0.20 na na D

δ13C of dissolved carbonates3 82081 na 1-sigma 0.05 na na D

Isotope ratios (atom ratio)

Strontium isotope ratio 

(87Sr/86Sr)4

75978 na MU 0.00005 na na D

Radioactive constituents (percent modern)

Carbon-145 49933 14762-75-5 MU 0.0015 na na D

Radioactive constituents (pCi/L)

Radon-2226 82303 14859-67-7 na CSU Prop. MCLUS

7

300 (4,000) D

Tritium8 07000 10028-17-8 MRL 1 MCL-CA 20,000 D

Gross alpha particle activity, 

72-hour and 30-day counts9

62636, 

62639

12587-46-1 ssLC CSU MCL-US 15 D

Gross beta particle activity, 

72-hour and 30-day counts9

62642, 

62645

12587-47-2 ssLC CSU MCL-CA 50 D

Radium-2269 09511 13982-63-3 ssLC CSU MCL-US 105 D

Radium-2289 81366 15262-20-1 ssLC CSU MCL-US 105 D

Uranium-2349 22610 13966-29-5 ssLC CSU MCL-CA 1120 D

Uranium-2359 22620 15117-96-1 ssLC CSU MCL-CA 1120 D

Uranium-2389 22603 7440-61-1 ssLC CSU MCL-CA 1120 D

Table 3I. Isotopic and radioactive constituents, comparative thresholds, and reporting information for laboratories.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as 

of June 1, 2008. Stable isotope ratios are reported in the standard delta notation (δ), the ratio of the abundance of a heavier isotope to the more common lighter 

isotope of that element, relative to a standard reference material. Threshold type: MCL-CA, California Department of Public Health maximum contaminant 

level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: H, hydrogen:, O, oxygen; C, carbon; Sr, strontium; 

CAS, Chemical Abstract Service; CSU, 1-sigma combined standard uncertainty; CV, critical value; MRL, minimum reporting level; MU, method uncertainty; 

na, not available; pCi/L, picocurie per liter; Prop., proposed; ssLC, sample-specific critical level; D, detected in groundwater samples (tables 11 and 12)]

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

USGS Stable Isotope Laboratory, Reston, Virginia.

3

University of Waterloo (contract laboratory).

4

USGS Metals Isotope Research Laboratory, Menlo Park, California.

5

University of Arizona, Accelerator Mass Spectrometry Laboratory (contract laboratory).

6

USGS National Water Quality Laboratory.

7

Two MCLs have been proposed for Radon-222. The proposed alternative MCL is in parentheses.

8

USGS Tritium Laboratory, Menlo Park, California.

9

Eberline Analytical Services (contract laboratory).

10The MCL-US threshold for radium is the sum of radium-226 and radium-228..

11The MCL-CA threshold for uranium is the sum of uranium-234, uranium-235, and uranium-238.
36 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Constituent

USGS 

parameter 

code

CAS number MU 

(percent)

Reporting 

units

Threshold 

type1

Threshold 

value 

(pCi/L)

Helium-3/Helium-4 61040 na/7440-59-7 0.75 atom ratio na na

Argon 85563 7440-37-1 2 cm3

 STP/g na na

Helium-4 85561 7440-59-7 2 cm3

 STP/g na na

Krypton 85565 7439-90-9 2 cm3

 STP/g na na

Neon 61046 7440-01-09 2 cm3

 STP/g na na

Xenon 85567 7440-63-3 2 cm3

 STP/g na na

Tritium 07000 10028-17-8 1 pCi/L MCL-CA 20,000

Table 3J. Noble gases and tritium, comparison thresholds and reporting information for the Lawrence Livermore National Laboratory

[The five-digit U.S. Geological survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values 

as of June 1, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level. Other abbreviations: CAS, Chemical 

Abstract Service; MU, method uncertainty; na, not available; cm3 STP/g, cubic centimeter of gas at standard temperature and pressure per gram of water; pCi/L, 

picocurie per liter]

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

Constituent

USGS 

parameter 

code

Primary source MDL Threshold 

type

Threshold 

value Detection

F-specific coliphage 99335 Sewage and animal waste 

indicator

na TT-US 99.99 percent killed/inactivated —

Somatic coliphage 99332 Sewage and animal waste 

indicator

na TT-US 99.99 percent killed/inactivated —

Table 3K. Microbial constituents, comparison thresholds, and reporting information for the U.S. Geological Survey (USGS) Ohio 

Microbiology Laboratory parameter codes 99335 and 99332.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of June 1, 2008. 

Threshold type: TT-US, U.S. Environmental Protection Agency treatment technique - a required process intended to reduce the level of contamination in 

drinking water. Other abbreviations: MDL, method detection limit; na, not available; —, not detected]
Tables 37

Table 4. Water-quality indicators in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June–September 2007.—Continued

[The five digit number below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. 

GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; 

TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. 

Thresholds and threshold values as of June 1, 2008. Threshold type: SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant 

level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: A, average of two replicate values; 

°C, degrees Celsius; E, estimated value; RL, reporting limit; mg/L, milligram per liter; nc, sample not collected; na, not available; μS/cm, microsiemens per 

centimeter; CaCO3, calcium carbonate; <, less than; >, greater than; *, value above threshold value or outside threshold range; **, value above upper threshold 

value]

GAMA well 

identification 

number

Dissolved 

oxygen, 

field 

(mg/L) 

(00300) 

Water 

temperature, 

field 

(°C) 

(00010)

pH, 

field 

(standard 

units) 

(00400)

pH, 

lab 

(standard 

units) 

(00403)

Specific 

conductance,

 field 

(μS/cm 

at 25°C) 

(00095)

Specific 

conductance, 

 lab 

(μS/cm 

at 25°C) 

(90095)

Alkalinity, 

field 

(mg/L as 

CaCO3

) 

(29802)

Alkalinity, 

lab 

(mg/L as 

CaCO3

) 

(29801)

Threshold 

type na na SMCL-US SMCL-US SMCL-CA SMCL-CA na na

Threshold 

level na na <6.5 or >8.5 <6.5 or >8.5 1

900 (1,600) 1900 (1,600) na na

[RL] [0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [1] [1]

Grid wells

TMART-01 6.5 13.5 8.2 8.0 173 176 A77 82

TMART-02 6.6 17.5 8.4 8.3 162 162 nc 86

TMART-03 0.2 15.5 7.9 8.0 330 327 nc 155

TMART-04 E10 12.0 8.0 8.0 193 199 nc 89

TMART-05 7.2 18.0 7.9 7.8 314 329 nc 97

TMART-06 8.6 8.5 7.0 7.2 187 192 A83 88

TMART-07 4.1 13.0 6.7 *6.3 234 239 nc 58

TMART-08 6.0 17.0 8.2 8.0 332 338 nc 74

TMART-09 9.6 10.0 6.9 7.5 172 178 nc 94

TMART-10 6.1 12.5 8.0 8.2 167 181 nc 92

TMART-11 9.4 10.0 7.0 7.2 166 169 nc 57

TMART-12 8.8 11.0 8.1 8.1 133 142 nc 72

TMART-13 8.9 15.5 8.0 7.8 248 256 nc 105

TMART-14 3.9 18.5 7.5 7.8 260 267 nc 119

TROCK-01 6.2 12.5 7.4 7.6 277 289 nc 86

TROCK-02 2.8 7.5 *6.0 7.6 47 50 nc 26

TROCK-03 8.1 18.0 7.6 7.8 221 237 nc 126

TROCK-04 11.9 5.0 7.3 7.8 92 96 nc 50

TROCK-05 10.7 6.5 7.2 7.5 137 140 nc 75

TROCK-06 9.1 8.5 6.9 7.2 176 179 nc 96

TROCK-07 6.8 9.0 6.7 6.9 123 128 nc 52

TROCK-08 9.5 6.5 *5.5 7.0 15 18 nc 10

TROCK-09 8.1 14.5 *5.9 *6.4 31 34 nc 18

TROCK-10 7.6 12.5 7.4 7.7 169 175 nc 93

TROCK-11 6.0 9.0 6.5 6.8 131 135 nc 64

TROCK-12 0.5 12.5 *5.8 *6.1 **2,820 **2,900 nc 553

TROCK-13 12.6 12.5 7.3 7.5 *1,550 **1,660 A753 798

Table 4. Water-quality indicators in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June–September 2007.

[The five digit number below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. 

GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; 

TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level; 

SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: A, average of two replicate values; 

°C, degrees Celsius; E, estimated value; RL, reporting limit; mg/L, milligram per liter; nc, sample not collected; na, not available; μS/cm, microsiemens per 

centimeter; CaCO3, calcium carbonate; <, less than; >, greater than; *, value above threshold value or outside threshold range; **, value above upper threshold 

value]
38 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table 4. Water-quality indicators in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June–September 2007.—Continued

[The five digit number below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. 

GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; 

TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. 

Thresholds and threshold values as of June 1, 2008. Threshold type: SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant 

level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: A, average of two replicate values; 

°C, degrees Celsius; E, estimated value; RL, reporting limit; mg/L, milligram per liter; nc, sample not collected; na, not available; μS/cm, microsiemens per 

centimeter; CaCO3, calcium carbonate; <, less than; >, greater than; *, value above threshold value or outside threshold range; **, value above upper threshold 

value]

GAMA well 

identification 

number

Dissolved 

oxygen, 

field 

(mg/L) 

(00300) 

Water 

temperature, 

field 

(°C) 

(00010)

pH, 

field 

(standard 

units) 

(00400)

pH, 

lab 

(standard 

units) 

(00403)

Specific 

conductance,

 field 

(μS/cm 

at 25°C) 

(00095)

Specific 

conductance, 

 lab 

(μS/cm 

at 25°C) 

(90095)

Alkalinity, 

field 

(mg/L as 

CaCO3

) 

(29802)

Alkalinity, 

lab 

(mg/L as 

CaCO3

) 

(29801)

Threshold 

type na na SMCL-US SMCL-US SMCL-CA SMCL-CA na na

Threshold 

level na na <6.5 or >8.5 <6.5 or >8.5 1

900 (1,600) 1900 (1,600) na na

[RL] [0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [1] [1]

TTAHO-01 4.9 11.0 7.5 7.6 293 311 nc 114

TTAHO-02 7.6 14.5 8.1 8.1 199 206 A88 108

TTAHO-03 8.8 9.0 *6.1 6.7 71 76 nc 41

TTAHO-04 9.5 7.0 6.7 6.9 106 117 nc 61

TTAHO-05 6.9 9.0 7.6 7.8 135 138 nc 71

TTAHO-06 5.2 15.0 *9.0 *8.9 116 122 A39 50

TTAHO-07 8.4 9.0 8.0 8.1 73 76 nc 39

TTAHO-08 4.2 10.5 7.6 7.8 202 207 nc 70

TTAHO-09 5.7 10.5 8.1 8.2 118 123 nc 59

TTAHO-10 5.3 11.5 *8.6 *8.6 77 80 A35 40

TTAHO-11 0.2 15.0 *6.3 *6.4 **2,080 **1,910 A426 473

TTAHO-12 4.8 11.0 6.5 6.8 144 147 nc 37

TTAHO-13 0.8 12.5 *6.2 6.9 80 85 A5 39

TTAHO-14 9.6 11.5 *9.0 *9.1 64 70 nc 34

Understanding wells

TMARTU-01 7.9 11.0 7.9 7.9 180 187 A87 95

TROCKU-01 16.2 8.0 7.3 7.7 105 109 nc 58

TROCKU-02 5.3 19.0 8.0 8.1 171 173 nc 90

TTAHOU-01 4.5 11.5 *8.8 *8.7 156 161 nc 61

TTAHOU-02 3.7 10.0 7.4 7.5 116 120 nc 55

TTAHOU-03 1.2 13.5 *9.0 *9.0 109 112 nc 46

TTAHOU-04 9.0 9.0 6.6 6.8 131 135 nc 52

TTAHOU-05 5.8 18.0 *9.2 *9.2 68 70 A28 33

TTAHOU-06 6.6 11.0 8.4 8.4 108 112 nc 46

TTAHOU-07 1.6 11.5 7.3 7.7 95 97 nc 48

TTAHOU-08 11.4 12.5 *6.1 7.7 62 68 nc 32

1

The SMCL-CA for specific conductance has recommended and upper threshold values. The upper value is shown in parentheses.
Tables 39

Table 5. Volatile organic compounds (VOC), and gasoline oxygenates and degradates detected in samples collected for the Tahoe–

Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed, but only samples with detections are listed. Analytes are grouped by primary use or source and listed 

in order of decreasing detection frequency in the 41 grid wells within each group. All analytes are listed in tables 3A,B. GAMA well identification number: 

TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding 

well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA; California Department of Public Health maximum contaminant level; NL-CA, California Department 

of Public Health notification level. Other abbreviations: E, estimated value; V, analyte detected in blanks and excluded from the dataset of groundwater quality 

results; LRL, laboratory reporting level; DBP, disinfection by-product; na, not available; μg/L, microgram per liter; —, not detected; 

*, value greater than threshold value]

GAMA well identification 

number

DBP Solvent Gasoline oxygenate Sulfide

VOC 

detections per 

well1

Chloroform, 

(μg/L) 

(32106)

Bromodichloromethane, 

(μg/L) 

(32101)

Perchloroethene 

(PCE), 

(μg/L) 

(34475)

1,1,1-Trichloroethane, 

(μg/L) 

(34506)

Trichloroethene 

(TCE), 

(μg/L) 

(39180)

Methyl 

tert-butyl 

ether 

(MTBE), 

(μg/L) 

(78032)

Diisopropyl 

ether, 

(μg/L) 

(81577)

Carbon 

disulfide, 

(μg/L) 

(77041)

[LRL] [0.04, 

0.02] [0.04] [0.04] [0.04, 0.02] [0.02] [0.1] [0.06] [0.06]

Threshold type2 MCL-US MCL-US MCL-US MCL-US MCL-US MCL-CA na NL-CA

Threshold level 3

80 380 5 200 5 13 na 160

Grid wells

TMART-034 0.28 0.11 — — — — — — 2

TMART-04 E0.03 — — — — E0.04 — — 1

TMART-06 E0.07 — E0.03 — — — — — 2

TMART-09 1.12 E0.04 — — — — — — 2

TMART-11 E0.03 — — — — — — — 1

TROCK-07 E0.01 — — — — — 0.1 — 2

TROCK-094 E0.01 — — — — — — — 1

TROCK-134 E0.03 — — — — — — — 1

TTAHO-02 — — E0.05 — — — — — 1

TTAHO-05 — — E0.02 — — — — — 1

TTAHO-06 E0.02 — *19.5 — E0.03 — — — 3

TTAHO-07 — — E0.03 — — — — — 1

TTAHO-08 0.1 — 0.24 E0.03 — 0.1 — — 4

TTAHO-11 — — — — — — — E0.35 1

TTAHO-12 0.28 E0.04 E0.04 — — 0.8 — — 4

Number of detections 11 3 7 1 1 3 1 1

Detection frequency (percentage) 27 7 17 2 2 7 2 2 5

37

Understanding wells

TTAHOU-01 0.12 — — — — 0.3 — — 2

TTAHOU-02 E0.01 — — — — — — — 1

TTAHOU-046 E0.05 — — — — 0.1 — — 2

TTAHOU-06 E0.07 — E0.04 — — — — — 2

TTAHOU-07 — — E0.01 — — — — — 1

1

All detections of the following three compounds were V-coded: tetrahydrofuran (TROCK-12, -13), toluene (TMART-10, TROCK-12), and 1,2,4-trimethylbenzene (TMART-10, -13; TMARTU-01; TROCK-08, -09, -10, -11; TTAHO-05, -07, -08, -09, -10, -12, -13, -14; TTAHOU-01, -02, -03, -06, -07).

2

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

3

The MCL-US threshold for trihalomethanes is the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.

4

The sampling point on the well was downstream of the point where hypochlorite disinfection solution was added. The disinfection system was shut off before 

the samples were collected.

5

Frequency of detection of at least one volatile organic compound (VOC) in the grid wells. Detections assigned V remark codes are not included.

6

Well was sampled for VOCs on 4/3/2008.
40 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

GAMA well identification number

Herbicide Herbicide 

degradate Insecticide

Pesticide 

detections 

per well

Atrazine 

(μg/L) 

(39632)

Deethylatrazine 

(μg/L) 

(04040)

Dicrotophos 

(μg/L) 

(38454)

[LRL] [0.007] [0.014] [0.0843]

Threshold type1 MCL-CA na na

Threshold level 1 na na

Grid wells

TMART-07 0.012 E0.008 — 2

TMART-11 E0.004 E0.003 E0.03 3

Number of detections 2 2 1

Detection frequency (percentage) 5 5 2 2

5

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA 

when the MCL-CA is lower than the MCL-US or no MCL-US exists.

2

Frequency of detecting at least one pesticide in the grid wells.

Table 6. Pesticides and pesticide degradates detected in samples collected for the Tahoe–Martis Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed, but only samples with detections are listed. Analytes 

are grouped by primary use or sources and listed in order of decreasing detection frequency in the 41 grid wells within each group. All 

analytes are listed in table 3C. GAMA well identification number: TMART, Martis study area grid well. Thresholds and threshold 

values as of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCLUS, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory 

reporting level, na, not available; μg/L, microgram per liter; —, not detected]
Tables 41

Table 7. Nutrients detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, June–September 2007.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed, but only samples with detections are listed. All analytes are listed in table 3F. Values less than 

the concentrations measured in field blanks (table A3A) are reported with a less than or equal to sign (≤). GAMA well identification number: TMART, 

Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; 

TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. 

Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; MCL-US; U.S. Environmental Protection Agency maximum 

contaminant level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level. Other abbreviations: E, estimated value; LRL, laboratory 

reporting level; na, not available; mg/L, milligram per liter; ≤, less than or equal to; —, not detected]

GAMA well 

identification 

number

Ammonia, 

as nitrogen 

(mg/L) 

(00608)

Nitrite plus nitrate,

 as nitrogen 

(mg/L) 

(00631)

Nitrite, 

as nitrogen 

(mg/L) 

(00613)

Total nitrogen 

(nitrate + nitrite + 

ammonia + 

organic-N), 

as nitrogen 

(mg/L) 

(62854)

Orthophosphate, 

as phosphorus 

(mg/L) 

(00671)

[LRL] [0.02] [0.06] [0.002] [0.06] [0.006]

Threshold type1 HAL-US MCL-US MCL-US na na

Threshold level 2

24.7 10 1 na na

Grid wells

TMART-01 0.037 0.25 E0.001 0.28 0.216

TMART-02 — 0.14 — 0.15 0.029

TMART-03 0.141 — — 0.14 0.140

TMART-04 — 0.44 — 0.49 0.070

TMART-05 — 0.07 — 0.13 0.325

TMART-06 — 0.90 — 0.89 0.043

TMART-07 — 0.22 — 0.25 0.026

TMART-08 — 0.19 — 0.21 0.023

TMART-09 — 0.33 — 0.33 ≤0.004

TMART-10 — E0.05 — E0.05 0.045

TMART-11 — 1.14 E0.002 1.18 0.028

TMART-12 — 0.40 — 0.41 0.041

TMART-13 — E0.06 E0.001 3

E0.05 0.106

TMART-14 — E0.04 E0.001 3

E0.03 0.050

TROCK-01 — 0.08 — 3

0.07 0.024

TROCK-02 — — — — ≤0.006

TROCK-03 — 0.06 — 0.07 0.049

TROCK-04 — E0.04 — E0.04 0.048

TROCK-05 — — E0.001 E0.04 0.038

TROCK-06 — E0.06 E0.001 0.08 0.029

TROCK-07 — 0.11 — 0.11 0.099

TROCK-08 — — — — 0.010

TROCK-09 — — — — 0.015

TROCK-10 — 0.07 — 3

E0.05 0.020

TROCK-11 — E0.06 — 0.07 0.014

TROCK-12 ≤0.017 — E0.002 — 0.011

TROCK-13 — — E0.001 — 0.036

Table 7. Nutrients detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, June–September 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all 52 wells were analyzed, but only samples with detections are listed. All analytes are listed in table 3F. Values less than the concentrations measured in field blanks (table A3A) are reported with a less than or equal to sign (≤). GAMA well identification number: TMART, Martis study 

area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, 

Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: 

MCL-CA, California Department of Public Health maximum contaminant level; MCL-US; U.S. Environmental Protection Agency maximum contaminant level; 

HAL-US, U.S. Environmental Protection Agency lifetime health advisory level. Other abbreviations: E, estimated value; LRL, laboratory reporting level; na, 

not available; mg/L, milligram per liter; ≤, less than or equal to; —, not detected]
42 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table 7. Nutrients detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, June–September 2007.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed, but only samples with detections are listed. All analytes are listed in table 3F. Values less than 

the concentrations measured in field blanks (table A3A) are reported with a less than or equal to sign (≤). GAMA well identification number: TMART, 

Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; 

TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. 

Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; MCL-US; U.S. Environmental Protection Agency maximum 

contaminant level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level. Other abbreviations: E, estimated value; LRL, laboratory 

reporting level; na, not available; mg/L, milligram per liter; ≤, less than or equal to; —, not detected]

GAMA well 

identification 

number

Ammonia, 

as nitrogen 

(mg/L) 

(00608)

Nitrite plus nitrate,

 as nitrogen 

(mg/L) 

(00631)

Nitrite, 

as nitrogen 

(mg/L) 

(00613)

Total nitrogen 

(nitrate + nitrite + 

ammonia + 

organic-N), 

as nitrogen 

(mg/L) 

(62854)

Orthophosphate, 

as phosphorus 

(mg/L) 

(00671)

[LRL] [0.02] [0.06] [0.002] [0.06] [0.006]

Threshold type1 HAL-US MCL-US MCL-US na na

Threshold level 2

24.7 10 1 na na

TTAHO-01 — 0.20 — 0.21 0.105

TTAHO-02 — 0.18 E0.001 0.20 0.077

TTAHO-03 — — — — 0.032

TTAHO-04 — E0.04 — 3

E0.03 0.031

TTAHO-05 ≤0.015 0.06 — 0.07 0.064

TTAHO-06 — 0.59 — 0.61 0.016

TTAHO-07 — 0.13 — 0.13 0.153

TTAHO-08 — 0.89 — 0.92 0.044

TTAHO-09 — E0.06 — 0.07 0.090

TTAHO-10 — E0.03 — — 0.035

TTAHO-11 0.035 — 0.003 E0.03 0.034

TTAHO-12 — 0.30 E0.002 0.32 0.014

TTAHO-13 0.060 — — E0.05 0.024

TTAHO-14 — E0.04 E0.001 — 0.009

Understanding wells

TMARTU-01 — 0.11 — 0.12 0.059

TROCKU-01 — E0.05 — 3

E0.04 0.031

TROCKU-02 — E0.04 — E0.04 0.066

TTAHOU-01 — 0.46 — 0.48 0.031

TTAHOU-02 — 0.27 — 0.31 0.042

TTAHOU-03 — — — — 0.071

TTAHOU-04 — 0.75 E0.002 0.79 0.036

TTAHOU-05 — E0.05 — 3

E0.04 0.015

TTAHOU-06 — 0.96 — 0.96 0.022

TTAHOU-07 — 0.29 — 0.30 0.017

TTAHOU-08 ≤0.021 0.24 0.003 0.26 0.037

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

The HAL-US is 30 mg/L "as ammonia." To facilitate comparison to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L "as 

nitrogen."

3

Total nitrogen in these samples is less than the sum of the filtered nitrogen analytes and falls outside the U.S. Geological Survey National Water Quality 

Laboratory acceptance criterion of a 10 percent relative percent difference. However, the absolute difference is ≤0.02 mg/L.
Tables 43

Table 8. Major and minor ions and dissolved solids detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3G contains additional information about the analytes. GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level, na, not available; mg/L, milligram per liter; —, not detected; *, value 

above recommended threshold value; **, value above upper threshold value]

GAMA well 

identification 

number

Calcium 

(mg/L) 

(00915)

Magnesium 

(mg/L) 

(00925)

Potassium

 (mg/L) 

(00935)

Sodium 

(mg/L) 

(00930)

Bicarbonate1 

(mg/L)

Carbonate1

(mg/L)

Bromide 

(mg/L) 

(71870)

Chloride 

(mg/L) 

(00940)

Fluoride 

(mg/L) 

(00950)

Iodide 

(mg/L) 

(71865)

Silica 

(mg/L) 

(00955)

Sulfate 

(mg/L) 

(00945)

Total 

dissolved 

solids 

(TDS) 

(mg/L) 

(70300)

[LRL] [0.02] [0.014] [0.04] [0.2] [1] [1] [0.02] [0.12] [0.1] [0.002] [0.018] [0.18] [10]

Threshold type2 na na na na na na na SMCL-CA3 MCL-CA na na SMCL-CA3 SMCL-CA3

Threshold level na na na na na na na 250 (500) 2 na na 250 (500) 500 (1,000)

Grid wells

TMART-01 10.0 6.65 3.50 15.5 99 — — 5.85 0.12 0.009 33.8 1.11 118

TMART-02 11.0 6.47 3.25 13.2 103 1 — 0.93 E0.06 — 36.2 0.90 125TMART-03 10.1 7.71 4.62 52.2 187 1 E0.01 6.10 0.18 0.018 47.5 12.2 230

TMART-04 12.5 9.48 3.61 13.9 108 — 0.03 5.89 E0.06 E0.001 34.5 4.77 134

TMART-05 9.96 6.93 7.14 46.4 118 — 0.07 34.2 0.17 0.051 44.6 9.73 211

TMART-06 15.9 11.5 1.32 5.20 107 — — 6.21 — — 33.0 1.35 127

TMART-07 17.6 7.50 2.75 14.2 71 — E0.02 35.4 — E0.002 34.2 2.03 146TMART-08 28.3 4.70 2.72 27.6 89 — 0.09 49.4 — E0.001 27.8 14.8 202TMART-09 21.0 6.94 1.21 5.30 114 — — 0.42 — — 35.8 E0.12 125

TMART-10 16.6 5.50 4.39 9.44 111 1 — 0.44 E0.05 — 40.9 2.79 147

TMART-11 15.6 7.45 1.22 5.36 69 — E0.02 14.1 E0.06 — 33.0 0.50 133TMART-12 12.9 4.52 3.22 7.49 87 1 — 0.38 E0.05 — 45.7 0.20 100

TMART-13 11.1 8.77 4.61 28.1 127 — 0.02 11.7 0.11 — 41.8 8.62 164TMART-14 25.0 6.29 6.04 16.4 144 — — 2.75 E0.09 — 59.9 15.0 201

Table 8. Major and minor ions and dissolved solids detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3G contains additional information about the analytes. GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe 

study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level, na, not available; mg/L, milligram per liter; —, not detected; *, value above recommended threshold value; **, value above upper threshold value]
44 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program Table 8. Major and minor ions and dissolved solids detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued [The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3G contains additional information about the analytes. GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level, na, not available; mg/L, milligram per liter; —, not detected; *, value above recommended threshold value; **, value above upper threshold value] GAMA well identification number Calcium (mg/L) (00915) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Bicar- bonate1 (mg/L) Car- bonate1 (mg/L) Bromide (mg/L) (71870) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Iodide (mg/L) (71865) Silica (mg/L) (00955) Sulfate (mg/L) (00945) Total dissolved solids (TDS) (mg/L) (70300) [LRL] [0.02] [0.014] [0.04] [0.2] [1] [1] [0.02] [0.12] [0.1] [0.002] [0.018] [0.18] [10] Threshold type2 na na na na na na na SMCL-CA3 MCL-CA na na SMCL-CA3 SMCL-CA3 Threshold level na na na na na na na 250 (500) 2 na na 250 (500) 500 (1,000) TROCK-01 32.7 5.73 3.98 9.47 105

— E0.02 36.3

—

— 24.0 0.67 217

TROCK-02 5.19 1.11 1.63 2.32 32

—

— 0.23

—

— 16.3 0.47 40

TROCK-03 22.7 10.3 3.74 7.29 153

—

— 0.56 E0.05

— 51.3 0.40 188

TROCK-04 10.1 3.64 2.60 2.71 61

—

— 0.20

—

— 29.7 0.31 82

TROCK-05 16.1 5.07 3.30 4.50 91

—

— 0.19

—

— 37.2 0.19 117

TROCK-06 18.7 8.30 3.21 5.77 117

—

— 0.40

—

— 40.6 0.33 158

TROCK-07 12.8 2.54 1.67 7.22 63

—

— 7.76

—

— 34.8 0.29 81

TROCK-08 1.25 0.206 0.33 1.41 12

—

— 0.18

—

— 9.51 0.31 20

TROCK-09 3.45 0.307 0.66 2.34 22

—

— 0.29

—

— 17.6 0.22 40

TROCK-10 17.1 7.30 2.35 6.51 113

—

— 0.29

—

— 33.0 0.21 125

TROCK-11 17.8 2.85 2.27 3.31 78

—

— 0.55

—

— 28.1 5.17 102

TROCK-12 530 101 5.95 124 675

—

— 2.04 0.78 0.004 15.4 *1,390 **2,690

TROCK-13 21.7 10.3 12.7 348 971 1 — 13.0 0.61 0.016 31.8 123 **1,080
Tables 45

Table 8. Major and minor ions and dissolved solids detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3G contains additional information about the analytes. GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level, na, not available; mg/L, milligram per liter; —, not detected; *, value 

above recommended threshold value; **, value above upper threshold value]

GAMA well 

identification 

number

Calcium 

(mg/L) 

(00915)

Magnesium 

(mg/L) 

(00925)

Potassium

 (mg/L) 

(00935)

Sodium 

(mg/L) 

(00930)

Bicarbonate1 

(mg/L)

Carbonate1

(mg/L)

Bromide 

(mg/L) 

(71870)

Chloride 

(mg/L) 

(00940)

Fluoride 

(mg/L) 

(00950)

Iodide 

(mg/L) 

(71865)

Silica 

(mg/L) 

(00955)

Sulfate 

(mg/L) 

(00945)

Total 

dissolved 

solids 

(TDS) 

(mg/L) 

(70300)

[LRL] [0.02] [0.014] [0.04] [0.2] [1] [1] [0.02] [0.12] [0.1] [0.002] [0.018] [0.18] [10]

Threshold type2 na na na na na na na SMCL-CA3 MCL-CA na na SMCL-CA3 SMCL-CA3

Threshold level na na na na na na na 250 (500) 2 na na 250 (500) 500 (1,000)TTAHO-01 27.9 15.9 4.89 6.20 139 — — 27.4 — — 42.9 1.20 187

TTAHO-02 20.4 6.82 4.60 11.0 130 1 — 0.66 — — 43.3 0.24 173

TTAHO-03 8.06 1.07 0.94 6.12 50 — — 0.23 — — 32.9 E0.14 65

TTAHO-04 12.0 4.29 0.81 4.51 74 — — 0.23 — — 35.1 0.47 85

TTAHO-05 11.1 6.89 2.82 5.19 86 — — 0.41 — — 38.3 2.85 101

TTAHO-06 7.91 0.787 0.86 15.6 56 2 — 4.70 0.13 — 22.6 3.12 91

TTAHO-07 7.11 2.15 1.08 4.14 47 — — 0.61 — — 27.8 0.31 62

TTAHO-08 22.1 4.55 1.10 10.2 85 — 0.02 17.3 — — 25.1 2.88 138

TTAHO-09 16.5 2.03 1.01 3.98 71 1 — 0.21 — — 17.6 4.67 84

TTAHO-10 3.88 0.541 0.27 13.6 47 1 — 1.06 — — 18.3 2.02 56

TTAHO-11 95.7 38.7 7.83 284 577 — 0.63 *425 0.52 0.635 49.8 34.2 **1,310

TTAHO-12 14.8 2.91 1.31 6.60 45 — — 19.0 — — 20.9 2.49 118

TTAHO-13 8.28 1.76 1.00 5.16 48 — — 2.68 — — 32.8 — 75

TTAHO-14 6.45 0.014 0.84 7.92 36 2 — 0.39 0.11 — 11.8 1.52 44
46 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program Table 8. Major and minor ions and dissolved solids detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued [The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3G contains additional information about the analytes. GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level, na, not available; mg/L, milligram per liter; —, not detected; *, value above recommended threshold value; **, value above upper threshold value] GAMA well identification number Calcium (mg/L) (00915) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Bicar- bonate1 (mg/L) Car- bonate1 (mg/L) Bromide (mg/L) (71870) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Iodide (mg/L) (71865) Silica (mg/L) (00955) Sulfate (mg/L) (00945) Total dissolved solids (TDS) (mg/L) (70300) [LRL] [0.02] [0.014] [0.04] [0.2] [1] [1] [0.02] [0.12] [0.1] [0.002] [0.018] [0.18] [10] Threshold type2 na na na na na na na SMCL-CA3 MCL-CA na na SMCL-CA3 SMCL-CA3 Threshold level na na na na na na na 250 (500) 2 na na 250 (500) 500 (1,000) Understanding wells TMARTU-01 11.6 8.84 4.45 12.2 115

—

— 1.70

—

— 39.5 1.54 130

TROCKU-01 10.8 3.83 2.48 4.03 70

—

— 0.28

—

— 36.7 0.20 96

TROCKU-02 7.95 6.49 7.42 14.8 108 1 — 0.42 E0.06

— 62.1 1.29 144

TTAHOU-01 14.1 0.912 1.96 17.0 71 2 — 10.3 E0.08

— 23.8 2.44 106

TTAHOU-02 12.9 2.67 0.52 6.83 67

—

— 2.98

—

— 25.7 1.44 90

TTAHOU-03 4.94 0.178 0.44 19.2 51 2 — 2.57 0.26 E0.002 18.7 6.96 75

TTAHOU-04 14.5 2.62 1.51 7.38 63

—

— 5.82

—

— 25.2 3.69 98

TTAHOU-05 6.28 E0.013 0.54 8.23 34 2 — 0.35 0.10

— 11.7 1.98 42

TTAHOU-06 14.6 0.30 0.70 7.01 55 1 — 3.29

—

— 19.6 2.21 78

TTAHOU-07 11.1 1.78 0.77 5.62 58

—

— 1.19

—

— 25.7 0.50 81

TTAHOU-08 6.02 1.16 1.13 5.28 39

—

— 1.44 E0.05

— 31.3 0.46 66

1Bicarbonate and carbonate concentrations were calculated from the laboratory alkalinity and pH values (table 4) using the advanced speciation method (http://or.water.usgs.gov/alk/methods.html) 

with pK1 = 6.35, pK2 = 10.33, and pKW = 14. pKa, pK2, and pKW are the minus logarithms of the equilibrium constants for the first ionization of carbonic acid, the second ionization of carbonic acid, 

and the first ionization of water, respectively.

2Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists.3The SMCL-CA for chloride, sulfate, and total dissolved solids have recommended and upper threshold values. The upper value is shown in parentheses.
Tables 47

Table 9. Trace elements detected in groundwater samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, June–September 2007.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3G contains additional information about the analytes. Values less than the study reporting 

limit are reported with a less than or equal to sign (≤). GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study 

area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; 

TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of 

Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of 

Public Health notification level; AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health 

advisory level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: NWQL, U.S. Geological 

Survey National Water Quality Laboratory; BQS, U.S. Geological Survey Office of Water Quality Branch of Quality Systems; NWIS, U.S. Geological Survey 

National Water Information System database; E, estimated value; LRL, laboratory reporting level; SRL, study reporting limit; na, not available; μg/L, microgram per liter; —, not detected; *, value above threshold value; ≤, less than or equal to]

GAMA well 

identification 

number

Aluminum 

(μg/L) 

(01106)

Antimony 

(μg/L) 

(01095)

Arsenic 

(μg/L) 

(01000)

Barium 

(μg/L) 

(01005)

Beryllium 

(μg/L) 

(01010)

Boron 

(μg/L) 

(01020)

Cadmium 

(μg/L) 

(01025)

Chromium 

(μg/L) 

(01030)

Cobalt 

(μg/L) 

(01035)

Copper 

(μg/L) 

(01040)

Iron 

(μg/L) 

(01046)

Lead 

(μg/L) 

(01049)

[LRL] or [SRL]1 2 [1.6] [0.06] [0.12] 2 [0.36] [0.06] [8] [0.04] 2 [0.42] [0.04] 2 [1.7] 2 [6] 2 [0.65]

Threshold type3 MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US

Threshold level 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300 15

Grid wells

TMART-01 2.5 E0.03 2.4 8 — 128 — 0.65 0.1 ≤1.2 14 ≤0.11

TMART-02 4.2 E0.04 0.8 7 — 13 — 2.1 — ≤0.22 — ≤0.23

TMART-03 — — *30.8 53 — 401 — — — ≤1.6 120 —

TMART-04 ≤1.1 0.07 *11.5 25 — 91 — 1.2 — ≤0.41 — ≤0.27

TMART-05 2.4 0.07 *16.7 23 — 654 — 0.58 — 2.2 20 ≤0.27

TMART-06 1.7 — 1.6 12 — 24 — 1.0 — ≤0.89 — ≤0.14

TMART-07 — — 0.38 25 — 9 — ≤0.19 E0.02 ≤0.58 — ≤0.24

TMART-08 1.9 0.06 8.1 6 — 334 — 0.54 — ≤0.22 6 —

TMART-09 ≤0.9 — — 12 — — — ≤0.30 — ≤1.1 — ≤0.12

TMART-10 — E0.03 1.0 55 — E5 — ≤0.38 — — — ≤0.16

TMART-11 ≤1.0 — 0.66 14 — — — 0.69 — ≤0.63 7 ≤0.16

TMART-12 ≤1.4 E0.04 0.52 29 — E8 — 0.48 — — 6 —

TMART-13 5.4 0.06 *48 31 — 279 — 0.56 — ≤1.5 8 ≤0.39

TMART-14 2.1 E0.05 1.6 88 — 36 — ≤0.23 — ≤1.4 — ≤0.51

TROCK-01 — 0.10 0.21 2 — — — — — ≤0.69 14 ≤0.47

TROCK-02 5.7 E0.05 E0.08 4 — — — ≤0.17 — 3.1 — ≤0.22

TROCK-03 — — 0.31 101 — — — ≤0.11 — ≤0.54 — ≤0.24

TROCK-04 — — 0.15 30 — — — ≤0.23 — ≤0.57 — ≤0.20

TROCK-05 ≤0.8 — E0.07 39 — — — 0.51 — ≤0.59 — ≤0.34

TROCK-06 8.3 — E0.09 25 — — — 1.2 — ≤0.77 ≤3 ≤0.45

TROCK-07 — — 1.7 17 — — — ≤0.17 — 4.0 — ≤0.18

TROCK-08 3.3 E0.03 — 5 — — E0.02 — — 11.3 — ≤0.64

TROCK-09 ≤1.2 — — E0.9 — — — ≤0.10 — 5.4 ≤3 ≤0.45

TROCK-10 ≤1.0 E0.03 0.59 9 — 8 — ≤0.31 — 2.3 — ≤0.25

TROCK-11 — 0.07 2.5 4 — E4 0.08 ≤0.14 — 10.9 ≤5 1.03

TROCK-12 32.1 — *14.9 8 0.82 84 E0.05 ≤0.28 0.95 5.1 *4,560 1.16

TROCK-13 1.9 0.07 *31.1 13 — *1,830 0.08 ≤0.07 E0.03 2.5 ≤4 ≤0.17

TTAHO-01 2.0 E0.04 0.24 56 — E6 — ≤0.24 E0.02 ≤0.70 86 ≤0.07

TTAHO-02 2.0 E0.05 0.53 52 — 9 E0.02 ≤0.21 — ≤0.32 — ≤0.44

TTAHO-03 — — 0.25 14 — — — ≤0.34 — 2.2 — ≤0.55

TTAHO-04 — E0.04 1.6 6 — — — 1.6 — ≤1.0 — ≤0.34

TTAHO-05 ≤1.5 — 2 11 — E7 — 0.45 — ≤0.76 ≤5 ≤0.20

TTAHO-06 4.3 0.26 7.2 3 — 35 — 0.96 — — — ≤0.35

Table 9. Trace elements detected in groundwater samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, June–September 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all 52 wells were analyzed. Table 3G contains additional information about the analytes. Values less than the study reporting limit are 

reported with a less than or equal to sign (≤). GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid 

well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, 

Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health 

maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health 

notification level; AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; 

SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: NWQL, U.S. Geological Survey National 

Water Quality Laboratory; BQS, U.S. Geological Survey Office of Water Quality Branch of Quality Systems; NWIS, U.S. Geological Survey National Water 

Information System database; E, estimated value; LRL, laboratory reporting level; SRL, study reporting limit; na, not available; μg/L, microgram per liter; —, 

not detected; *, value above threshold value; ≤, less than or equal to]
48 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table 9. Trace elements detected in groundwater samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, June–September 2007.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3G contains additional information about the analytes. Values less than the study reporting 

limit are reported with a less than or equal to sign (≤). GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study 

area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; 

TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of 

Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of 

Public Health notification level; AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health 

advisory level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: NWQL, U.S. Geological 

Survey National Water Quality Laboratory; BQS, U.S. Geological Survey Office of Water Quality Branch of Quality Systems; NWIS, U.S. Geological Survey 

National Water Information System database; E, estimated value; LRL, laboratory reporting level; SRL, study reporting limit; na, not available; μg/L, microgram per liter; —, not detected; *, value above threshold value; ≤, less than or equal to]

GAMA well 

identification 

number

Aluminum 

(μg/L) 

(01106)

Antimony 

(μg/L) 

(01095)

Arsenic 

(μg/L) 

(01000)

Barium 

(μg/L) 

(01005)

Beryllium 

(μg/L) 

(01010)

Boron 

(μg/L) 

(01020)

Cadmium 

(μg/L) 

(01025)

Chromium 

(μg/L) 

(01030)

Cobalt 

(μg/L) 

(01035)

Copper 

(μg/L) 

(01040)

Iron 

(μg/L) 

(01046)

Lead 

(μg/L) 

(01049)

[LRL] or [SRL]1 2 [1.6] [0.06] [0.12] 2 [0.36] [0.06] [8] [0.04] 2 [0.42] [0.04] 2 [1.7] 2 [6] 2 [0.65]

Threshold type3 MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US

Threshold level 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300 15

TTAHO-07 ≤1.3 E0.04 1.5 4 — E4 — 1.2 — ≤0.41 — ≤0.06

TTAHO-08 ≤1.1 E0.05 0.84 18 — 11 — 0.54 — ≤1.0 — ≤0.18

TTAHO-09 ≤1.5 0.14 *13.8 3 — — — 1.7 — ≤0.25 21 ≤0.26

TTAHO-10 6.6 0.11 7.8 3 — E5 — 0.42 — ≤0.47 7 ≤0.06

TTAHO-11 6.2 E0.04 *142 39 E0.03 *5,120 — 1.2 0.98 ≤0.24 *15,400 —

TTAHO-12 — — E0.1 15 — E5 — ≤0.17 0.07 — *350 —

TTAHO-13 4.6 — E0.07 8 — — 0.04 0.78 0.3 — 11 —

TTAHO-14 8.5 0.17 1.2 3 — 15 0.06 ≤0.22 — — — ≤0.09

Understanding wells

TMARTU-01 ≤0.9 0.06 7.3 17 — 65 — 1.2 — ≤0.45 — ≤0.08

TROCKU-01 ≤1.2 — 0.16 32 — — — ≤0.10 — ≤0.61 — ≤0.16

TROCKU-02 1.8 0.11 3.9 8 — 26 — 0.71 — ≤0.31 ≤4 ≤0.07

TTAHOU-01 10.9 0.13 7.4 3 — 41 — ≤0.29 — ≤0.33 — ≤0.06

TTAHOU-02 ≤1.4 — 0.88 13 — E7 E0.02 0.62 — ≤1.0 11 ≤0.18

TTAHOU-03 4.9 0.25 *10.2 2 — 84 0.06 ≤0.13 — ≤0.21 7 —

TTAHOU-04 — E0.03 0.12 16 — E5 E0.02 0.43 — ≤1.6 — ≤0.25

TTAHOU-05 16.1 0.22 0.82 2 — 10 0.13 ≤0.21 — — — —

TTAHOU-06 4.0 0.14 0.38 4 — 8 — 0.51 E0.02 — — —

TTAHOU-07 ≤1.5 0.10 0.65 8 — — — ≤0.12 — ≤0.32 — —

TTAHOU-08 5.8 0.07 0.31 14 — — 0.08 ≤0.18 0.09 ≤1.4 E6 —
Tables 49

Table 9. Trace elements detected in groundwater samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, June–September 2007.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3G contains additional information about the analytes. Values less than the study reporting 

limit are reported with a less than or equal to sign (≤). GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study 

area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; 

TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of 

Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of 

Public Health notification level; AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health 

advisory level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: NWQL, U.S. Geological 

Survey National Water Quality Laboratory; BQS, U.S. Geological Survey Office of Water Quality Branch of Quality Systems; NWIS, U.S. Geological Survey 

National Water Information System database; E, estimated value; LRL, laboratory reporting level; SRL, study reporting limit; na, not available; μg/L, microgram per liter; —, not detected; *, value above threshold value; ≤, less than or equal to]

GAMA well 

identification 

number

Lithium 

(μg/L) 

(01130)

Manganese 

(μg/L) 

(01056)

Molybdenum 

(μg/L) 

(01060)

Nickel 

(μg/L) 

(01065)

Selenium 

(μg/L) 

(01145)

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057)

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

Vanadium 

(μg/L) 

(01085)

Zinc 

(μg/L) 

(01090)

[LRL] or [SRL]1 [0.6] 2 [0.2] [0.12] 2 [0.36] [0.08] [0.4] [0.04] 2 [0.11] [0.04] 2 [0.11] 2

[4.8]2

Threshold type3 na SMCL-CA HAL-US MCL-CA MCL-US HAL-US MCL-US na MCL-US NL-CA SMCL-CA

Threshold level na 50 40 100 50 4,000 2 na 30 50 5,000

Grid wells

TMART-01 12.6 4.4 1.5 0.52 — 117 — 0.25 0.51 2.6 —

TMART-02 2.1 — 0.9 — 0.11 149 — ≤0.16 0.92 5.7 ≤3.8

TMART-03 15.3 *124 5.1 — — 134 — 0.56 E0.02 0.11 ≤1.4

TMART-04 13.3 ≤0.1 0.7 — — 132 — ≤0.20 0.71 7.3 —

TMART-05 43.6 7.8 7.0 0.51 — 97.3 — 0.72 0.63 3.4 ≤1.5

TMART-06 3.8 — 0.2 ≤0.04 — 394 — — 0.13 1.5 ≤0.32

TMART-07 1.5 1.1 0.3 ≤0.04 — 240 — E0.05 0.31 2.2 ≤0.47

TMART-08 21.5 ≤0.1 0.9 — — 199 — 0.86 0.47 2.1 ≤0.96

TMART-09 — — — ≤0.12 — 254 — — 0.23 1.1 12.5

TMART-10 0.8 — 0.3 — 0.12 192 — 1.4 0.96 4.4 9.6

TMART-11 1.9 0.2 E0.1 — E0.05 174 — — 0.09 1.8 64.0

TMART-12 5.8 ≤0.1 0.1 — — 137 — ≤0.08 0.68 6.4 ≤0.85

TMART-13 16.7 0.9 0.7 ≤0.07 — 158 — 0.26 0.61 12.9 28.3

TMART-14 5.2 0.2 1.0 ≤0.17 E0.06 319 — ≤0.09 1.14 8.1 ≤2.6

TROCK-01 4.5 1.4 2.9 ≤0.07 E0.04 245 — 0.33 9.83 0.86 5.5

TROCK-02 — 0.5 0.2 ≤0.09 — 30.1 — — 1.21 1.2 10.4

TROCK-03 2.6 — 0.2 — — 278 — E0.03 1.14 5.0 10.4

TROCK-04 — — — ≤0.04 — 70.4 — — 0.18 1.7 ≤1.6

TROCK-05 1.3 — — ≤0.04 — 155 — — 0.24 0.92 ≤1.5

TROCK-06 1.3 0.3 0.1 — — 240 — — 0.51 1.5 5.6

TROCK-07 4.0 — 0.3 ≤0.04 — 102 — ≤0.07 0.31 2.7 5.7

TROCK-08 — E0.2 — ≤0.24 — 14.1 — — 0.13 ≤0.10 12.4

TROCK-09 E0.6 0.5 — ≤0.12 — 37.3 — — 0.05 0.27 ≤2.1

TROCK-10 4.2 — — ≤0.09 — 207 — — 0.38 1.5 42.1

TROCK-11 2.1 0.2 1.4 0.53 0.47 51.4 — ≤0.06 0.14 1.3 16.5

TROCK-12 86.3 *1,340 0.4 3.0 — *5,600 — — — ≤0.06 66.9

TROCK-13 388 *87.4 *47.2 ≤0.26 — 659 E0.02 E0.04 0.8 0.08 49.1

TTAHO-01 E0.5 2.8 0.1 ≤0.07 — 274 — ≤0.06 0.87 3.3 13.0

TTAHO-02 3.3 — 0.5 — — 247 — E0.05 1.39 5.4 ≤1.1

TTAHO-03 1.8 ≤0.1 — — — 93 — — E0.03 1.1 6.5

TTAHO-04 E0.4 — E0.1 — E0.05 115 — — 0.06 2.6 ≤1.6

TTAHO-05 4.6 9.9 0.5 — — 138 — ≤0.21 0.18 1.2 6.5
50 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table 9. Trace elements detected in groundwater samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, June–September 2007.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3G contains additional information about the analytes. Values less than the study reporting 

limit are reported with a less than or equal to sign (≤). GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study 

area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; 

TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of 

Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of 

Public Health notification level; AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health 

advisory level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: NWQL, U.S. Geological 

Survey National Water Quality Laboratory; BQS, U.S. Geological Survey Office of Water Quality Branch of Quality Systems; NWIS, U.S. Geological Survey 

National Water Information System database; E, estimated value; LRL, laboratory reporting level; SRL, study reporting limit; na, not available; μg/L, microgram per liter; —, not detected; *, value above threshold value; ≤, less than or equal to]

GAMA well 

identification 

number

Lithium 

(μg/L) 

(01130)

Manganese 

(μg/L) 

(01056)

Molybdenum 

(μg/L) 

(01060)

Nickel 

(μg/L) 

(01065)

Selenium 

(μg/L) 

(01145)

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057)

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

Vanadium 

(μg/L) 

(01085)

Zinc 

(μg/L) 

(01090)

[LRL] or [SRL]1 [0.6] 2 [0.2] [0.12] 2 [0.36] [0.08] [0.4] [0.04] 2 [0.11] [0.04] 2 [0.11] 2

[4.8]2

Threshold type3 na SMCL-CA HAL-US MCL-CA MCL-US HAL-US MCL-US na MCL-US NL-CA SMCL-CA

Threshold level na 50 40 100 50 4,000 2 na 30 50 5,000

TTAHO-06 2.9 ≤0.1 10.5 — 0.09 37.2 — 9.2 25.3 3.0 —

TTAHO-07 1.8 E0.2 1.3 ≤0.10 E0.05 75 — 0.59 1.59 2.1 ≤0.73

TTAHO-08 5.4 — 6.4 ≤0.08 E0.04 207 — 1.4 14.2 2.2 ≤2.4

TTAHO-09 1.1 — 1.9 ≤0.10 0.72 66.3 — 0.91 1.63 7.0 ≤3.6

TTAHO-10 — 0.4 3.2 ≤0.03 E0.05 26.7 — 1.1 2.43 2.3 ≤1.5

TTAHO-11 474 *398 6.2 0.87 0.09 815 — 0.56 9.53 0.58 4.9

TTAHO-12 1.3 23.1 0.3 0.40 — 194 — — 0.1 0.34 ≤2.1

TTAHO-13 1.2 *70 0.4 0.80 — 147 — 0.38 0.07 0.52 5.0

TTAHO-14 — — *46.4 — E0.07 28.7 — 10.2 22.4 4.8 ≤1.3

Understanding wells

TMARTU-01 18.7 — 0.3 ≤0.03 — 137 — ≤0.11 0.74 6.8 ≤1.3

TROCKU-01 — — 0.1 — — 133 — — 0.3 1.5 ≤2.4

TROCKU-02 13.9 0.3 0.8 — 0.13 54.5 — 0.22 0.7 6.2 ≤3.9

TTAHOU-01 7.2 — 2.6 ≤0.06 — 52.6 — 2.8 14.4 1.8 —

TTAHOU-02 1.2 1.2 9.0 ≤0.06 E0.04 139 — 3.0 1.29 4.3 ≤1.7

TTAHOU-03 11.1 3.2 38.9 ≤0.04 E0.04 15.5 — 27.8 25.6 3.6 ≤0.75

TTAHOU-04 1.4 — 17.2 ≤0.05 E0.05 188 — 2.2 9.17 1.1 ≤2.2

TTAHOU-05 E0.5 E0.2 *85.3 0.59 0.09 39.2 — 15.4 *30.9 3.5 ≤1.2

TTAHOU-06 1.5 E0.2 1.3 ≤0.26 E0.05 97.1 — 1.7 *52.8 1.4 —

TTAHOU-07 1.0 1.7 1.0 ≤0.10 E0.06 139 — 2.5 3.88 2.3 ≤0.37

TTAHOU-08 2.1 15.9 0.3 1.2 — 102 — ≤0.18 0.06 0.68 14.2

1

Study reporting limits (SRL) were defined on the basis of the examination of field blanks collected in GAMA study units from May 2004 through January 

2008 (L.D. Olsen and M.S. Fram, U.S. Geological Survey, unpublished data, 2008).

2

Values equal to or less than the SRL are reported as less than or equal to the value reported by the laboratory (≤). Values reported with a ≤ symbol in this table 

have the following field comment included in the USGS NWIS database: Result is < or = reported value, based on quality control data (including but not limited 

to field blanks, source-solution blanks, trip blanks, NWQL set blanks, NWQL blank water certificates, and BQS Blind Blank Program data).

3

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.
Tables 51

Table 10. Species of inorganic arsenic, iron, and chromium detected in samples collected for the Tahoe–Martis Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued

[Data in this table were analyzed at U.S. Geological Survey (USGS) Trace Metal Laboratory in Boulder, Colorado using research methods and are not stored 

in the USGS National Water Information System database. Samples from all 52 wells were analyzed. Table 3H contains additional information about the 

analytes. Values less than the concentrations measured in field blanks (table A3A) are reported with a less than or equal to sign (≤). GAMA well identification 

number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area 

understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as 

of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection 

Agency maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: 

MDL, method detection limit, na, not available; μg/L, microgram per liter; —, not detected; *, value above threshold value]

GAMA well 

identification 

number

Iron 

(total) 

(μg/L) 

Iron(II) 

(μg/L) 

Arsenic

(total) 

(μg/L) 

Arsenic(III) 

(μg/L) 

Chromium 

(total) 

(μg/L) 

Chromium(VI) 

(μg/L) 

Threshold type1 SMCL-CA na MCL-US na MCL-CA na

Threshold level 300 na 10 na 50 na

[MDL] [2] [2] [0.5] [1] [1] [1]

Grid wells

TMART-01 18 9 2.2 — — —

TMART-02 — — 0.54 — 2 2

TMART-03 117 60 *25 6.3 — —

TMART-04 — — 9.8 — 1 —

TMART-05 18 14 *15 — — —

TMART-06 — — 1.3 — — —

TMART-07 — — — — — —

TMART-08 5 — 9.0 — — —

TMART-09 — — — — — —

TMART-10 — — 0.88 — — —

TMART-11 4 3 ≤0.56 — — —

TMART-12 — — — — — —

TMART-13 5 — *36 — — —

TMART-14 ≤2 — 1.0 — — —

TROCK-01 12 — — — — —

TROCK-02 — — — — — —

TROCK-03 — — — — — —

TROCK-04 — — — — — —

TROCK-05 4 — — — — —

TROCK-06 ≤2 — — — — —

TROCK-07 — — 1.4 — — —

TROCK-08 — — — — — —

TROCK-09 — — — — — —

TROCK-10 — — — — — —

TROCK-11 7 4 2.0 — — —

TROCK-12 *3,740 3,740 *14 9.2 — —

TROCK-13 4 — *41 — — —

TTAHO-01 80 20 — — — —

TTAHO-02 — — — — — —

TTAHO-03 — — — — — —

TTAHO-04 — — 1.2 — 1 1

TTAHO-05 5 3 1.6 1 — —

TTAHO-06 — — 5.9 — — —

TTAHO-07 — — 1.2 — 1 1

TTAHO-08 — — ≤0.53 — — —

Table 10. Species of inorganic arsenic, iron, and chromium detected in samples collected for the Tahoe–Martis Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June–September 2007.

[Data in this table were analyzed at U.S. Geological Survey (USGS) Trace Metal Laboratory in Boulder, Colorado using research methods and are not stored in 

the USGS National Water Information System database. Samples from all 52 wells were analyzed. Table 3H contains additional information about the analytes. 

Values less than the concentrations measured in field blanks (table A3A) are reported with a less than or equal to sign (≤). GAMA well identification number: 

TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding 

well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. 

Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: MDL, method detection 

limit, na, not available; μg/L, microgram per liter; —, not detected; *, value above threshold value]
52 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table 10. Species of inorganic arsenic, iron, and chromium detected in samples collected for the Tahoe–Martis Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued

[Data in this table were analyzed at U.S. Geological Survey (USGS) Trace Metal Laboratory in Boulder, Colorado using research methods and are not stored 

in the USGS National Water Information System database. Samples from all 52 wells were analyzed. Table 3H contains additional information about the 

analytes. Values less than the concentrations measured in field blanks (table A3A) are reported with a less than or equal to sign (≤). GAMA well identification 

number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area 

understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as 

of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection 

Agency maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: 

MDL, method detection limit, na, not available; μg/L, microgram per liter; —, not detected; *, value above threshold value]

GAMA well 

identification 

number

Iron 

(total) 

(μg/L) 

Iron(II) 

(μg/L) 

Arsenic

(total) 

(μg/L) 

Arsenic(III) 

(μg/L) 

Chromium 

(total) 

(μg/L) 

Chromium(VI) 

(μg/L) 

Threshold type1 SMCL-CA na MCL-US na MCL-CA na

Threshold level 300 na 10 na 50 na

[MDL] [2] [2] [0.5] [1] [1] [1]

TTAHO-09 ≤2 — 4.2 — 2 1

TTAHO-10 — — 2.7 — — —

TTAHO-11 *12,900 12,800 *150 110 — —

TTAHO-12 298 290 — — — —

TTAHO-13 9 5 — — — —

TTAHO-14 — — 0.97 1.1 — —

Understanding wells

TMARTU-01 — — 6.5 — — —

TROCKU-01 — — — — — —

TROCKU-02 — — 3.2 — — —

TTAHOU-01 — — 2.1 — — —

TTAHOU-02 — — — — — —

TTAHOU-03 5 3 5.6 — — —

TTAHOU-04 — — — — — —

TTAHOU-05 — — 1.0 — — —

TTAHOU-06 — — — — — —

TTAHOU-07 — — 0.77 — — —

TTAHOU-08 — — — — — — 1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.
Tables 53

Table 11. Stable isotope and strontium isotope ratios and tritium and carbon–14 activities detected in samples collected for the 

Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3I contains additional information about the analytes. Stable isotope ratios are reported in the 

standard delta notation (δ), the ratio of a heavier isotope to the more common lighter isotope of that element, relative to a standard reference material. GAMA 

well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, 

Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and 

threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: H, hydrogen; O, oxygen; C, carbon; Sr, strontium; nc, sample not collected; 

pCi/L, picocurie per liter; <, less than]

GAMA well 

identification 

number

δ2H of water 

(per mil) 

(82082)

δ18O of water 

(per mil) 

(82085)

Tritium 

(pCi/L) 

(07000)

δ13C of dissolved 

carbonates 

(per mil) 

(82081)

Carbon-14 

(percent modern)1

(49933)

87Sr/86Sr 

(atom ratio) 

(75978)

Threshold type2 na na MCL-CA na na na

Threshold level na na 20,000 na na na

Grid wells

TMART-01 –109 –14.89 4.2 –15.49 70 0.70524

TMART-02 –115 –15.44 1.6 –15.63 75 0.70501

TMART-03 –117 –15.53 <1 –15.29 29 0.70491

TMART-04 –108 –14.75 3.5 –16.32 72 0.70523

TMART-05 –111 –15.09 1.0 –13.29 40 0.70526

TMART-06 –105 –14.36 9.0 –16.88 97 0.70559

TMART-07 –92.3 –12.73 9.6 –17.53 101 0.70538

TMART-08 –107 –14.62 3.2 –17.16 82 0.70533

TMART-09 –105 –14.41 15.4 –16.45 100 0.70448

TMART-10 –105 –14.56 <1 –18.41 72 0.70488

TMART-11 –102 –13.86 12.8 –18.71 82 0.70532

TMART-12 –109 –14.77 <1 –17.27 85 0.70481

TMART-13 –110 –15.15 <1 –14.80 42 0.70524

TMART-14 –112 –14.98 <1 –16.65 71 0.70458

TROCK-01 –96.9 –13.61 12.5 –19.83 104 0.70563

TROCK-02 –95.8 –13.33 11.2 –18.05 106 0.70788

TROCK-03 –110 –15.02 <1 –16.06 81 0.70478

TROCK-04 –98.5 –13.85 9.0 –18.11 98 0.70527

TROCK-05 –101 –14.20 7.0 –18.04 97 0.70539

TROCK-06 –110 –15.07 5.1 –17.05 98 0.70532

TROCK-07 –99.7 –13.73 11.5 –18.04 98 0.70840

TROCK-08 –93.9 –13.25 9.3 –17.21 nc 0.70805

TROCK-09 –94.4 –13.44 9.0 –19.30 112 0.70902

TROCK-10 –106 –14.53 6.4 –18.46 87 0.70548

TROCK-11 –98.7 –13.46 10.2 –17.81 109 0.70863

TROCK-12 –104 –14.52 <1 –7.44 2 0.70548

TROCK-13 –112 –15.44 <1 –7.60 1 0.70545

TTAHO-01 –98.5 –13.66 10.2 –19.34 103 0.70533

TTAHO-02 –111 –15.32 <1 –16.77 82 0.70517

TTAHO-03 –100 –13.90 18.9 –17.86 100 0.70777

TTAHO-04 –97.5 –13.66 12.8 –18.74 96 0.70653

TTAHO-05 –106 –14.65 6.7 –17.40 88 0.70528

TTAHO-06 –109 –14.86 2.9 –19.24 83 0.70604

TTAHO-07 –106 –14.54 3.5 –18.67 91 0.70600

TTAHO-08 –107 –14.59 7.7 –19.56 91 0.70590

Table 11. Stable isotope and strontium isotope ratios and tritium and carbon–14 activities detected in samples collected for the Tahoe–

Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all 52 wells were analyzed. Table 3I contains additional information about the analytes. Stable isotope ratios are reported in the standard delta notation (δ), the ratio of a heavier isotope to the more common lighter isotope of that element, relative to a standard reference material. GAMA well 

identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis 

study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold 

values as of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: H, hydrogen; O, oxygen; C, carbon; Sr, strontium; nc, sample not collected; pCi/L, picocurie 

per liter; <, less than]
54 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table 11. Stable isotope and strontium isotope ratios and tritium and carbon–14 activities detected in samples collected for the 

Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3I contains additional information about the analytes. Stable isotope ratios are reported in the 

standard delta notation (δ), the ratio of a heavier isotope to the more common lighter isotope of that element, relative to a standard reference material. GAMA 

well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, 

Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and 

threshold values as of June 1, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: H, hydrogen; O, oxygen; C, carbon; Sr, strontium; nc, sample not collected; 

pCi/L, picocurie per liter; <, less than]

GAMA well 

identification 

number

δ2H of water 

(per mil) 

(82082)

δ18O of water 

(per mil) 

(82085)

Tritium 

(pCi/L) 

(07000)

δ13C of dissolved 

carbonates 

(per mil) 

(82081)

Carbon-14 

(percent modern)1

(49933)

87Sr/86Sr 

(atom ratio) 

(75978)

Threshold type2 na na MCL-CA na na na

Threshold level na na 20,000 na na na

TTAHO-09 –108 –14.72 <1 –19.09 76 0.70733

TTAHO-10 –105 –14.64 <1 –20.37 68 0.70667

TTAHO–11 –108 –14.82 4.5 –6.31 2 0.70646

TTAHO–12 –99.3 –13.86 6.7 –20.01 107 0.70568

TTAHO–13 –110 –14.98 4.8 –19.68 89 0.70590

TTAHO–14 –114 –15.57 <1 –17.98 84 0.70575

Understanding wells

TROCKU-01 –102 –14.31 5.1 –18.39 92 0.70490

TMARTU-01 –108 –15.01 1.6 –15.87 74 0.70532

TROCKU-02 –108 –14.92 <1 –16.41 71 0.70514

TTAHOU-01 –101 –13.92 9.0 –20.19 101 0.70766

TTAHOU-02 –111 –15.04 2.2 –19.02 87 0.70567

TTAHOU-03 –111 –15.13 <1 –17.66 57 0.70631

TTAHOU-04 –107 –14.59 9.9 –19.63 106 0.70595

TTAHOU-05 –111 –15.31 <1 –19.59 81 0.70620

TTAHOU-06 –113 –15.18 7.7 –17.90 97 0.70632

TTAHOU-07 –110 –15.15 13.1 –18.54 87 0.70626

TTAHOU-08 –104 –14.10 18.9 nc nc 0.70627

1

100-percent modern carbon is referenced to atmospheric carbon-14 production rates in 1950. Values of percent modern carbon can be greater than 

100 percent because the atmospheric production rate was much higher during the period of above-ground nuclear testing in the 1950s and 1960s.

2

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.
Tables 55

Table 12A. Uranium isotopes and radon-222 detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3I contains additional information about the analytes. Measured values less than the sample-specific critical level (ssLC) are reported as nondetections (—). GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, 

Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: CSU, 1-sigma combined standard uncertainty; pCi/L, picocurie per liter; nc, sample not collected; *, result above threshold value; ±, plus or minus]

GAMA well 

identification 

number

Uranium-234 

(pCi/L) 

(22610)

Uranium-235 

(pCi/L) 

(22620)

Uranium-238 

(pCi/L) 

(22603)

Radon-222 

(pCi/L) 

(82303)

Threshold type1 MCL-CA MCL-CA MCL-CA Proposed MCL-US

Threshold value

220 220 220 3300 (4,000)

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU4

Grid wells

TMART-01 0.343 ± 0.034 0.011 0.039 ± 0.013 0.011 0.170 ± 0.022 0.0089 1,020 ± 16

TMART-02 0.754 ± 0.052 0.0097 0.043 ± 0.015 0.0083 0.294 ± 0.030 0.0069 480 ± 11TMART-03 0.021 ± 0.011 0.0088 0.0162 ± 0.0065 0.0076 0.0134 ± 0.0080 0.0063 810 ± 13TMART-04 0.408 ± 0.036 0.0066 — 0.0079 0.203 ± 0.026 0.0066 1,740 ± 18

TMART-05 0.464 ± 0.040 0.0096 0.018 ± 0.011 0.0082 0.236 ± 0.027 0.0096 760 ± 14

TMART-06 0.068 ± 0.020 0.011 — 0.014 0.034 ± 0.015 0.011 870 ± 14

TMART-07 0.170 ± 0.026 0.0084 — 0.010 0.130 ± 0.022 0.0084 750 ± 13

TMART-08 0.541 ± 0.050 0.016 0.028 ± 0.014 0.011 0.149 ± 0.028 0.013 1,520 ± 17

TMART-09 0.160 ± 0.023 0.015 0.021 ± 0.011 0.0080 0.106 ± 0.017 0.0066 660 ± 13

TMART-10 0.663 ± 0.053 0.0084 0.0174 ± 0.0085 0.010 0.353 ± 0.038 0.0084 370 ± 11TMART-11 0.069 ± 0.017 0.0076 — 0.0092 0.042 ± 0.013 0.0076 1,030 ± 14

TMART-12 0.659 ± 0.077 0.017 — 0.021 0.252 ± 0.045 0.017 540 ± 12

TMART-13 0.346 ± 0.032 0.0091 0.020 ± 0.010 0.0078 0.216 ± 0.026 0.0091 1,360 ± 19

TMART-14 0.937 ± 0.060 0.011 0.020 ± 0.010 0.0079 0.374 ± 0.035 0.0065 660 ± 14

TROCK-01 4.59 ± 0.18 0.019 0.171 ± 0.028 0.0093 3.11 ± 0.13 0.015 1,950 ± 20

TROCK-02 0.525 ± 0.038 0.0055 0.0115 ± 0.0060 0.0067 0.408 ± 0.033 0.0055 nc

TROCK-03 1.109 ± 0.066 0.0078 0.0202 ± 0.0080 0.0094 0.533 ± 0.046 0.013 140 ± 9

TROCK-04 0.197 ± 0.025 0.0065 0.0168 ± 0.0065 0.0078 0.053 ± 0.014 0.0091 810 ± 14

TROCK-05 0.178 ± 0.028 0.014 — 0.0097 0.055 ± 0.014 0.0080 820 ± 14

TROCK-06 0.306 ± 0.031 0.011 0.0149 ± 0.0060 0.0070 0.182 ± 0.023 0.0057 350 ± 10

TROCK-07 0.156 ± 0.044 0.020 0.042 ± 0.021 0.024 0.139 ± 0.035 0.020 650 ± 12

TROCK-08 0.051 ± 0.015 0.0085 — 0.010 0.084 ± 0.019 0.0085 2,090 ± 23

TROCK-09 0.019 ± 0.013 0.010 — 0.0090 0.0350 ± 0.0095 0.0074 2,910 ± 26

Table 12A. Uranium isotopes and radon-222 detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3I contains additional information about the analytes. Measured values less than the sample-specific critical level (ssLC) are reported as nondetections (—). GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, 

Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: CSU, 1-sigma combined standard uncertainty; pCi/L, picocurie per liter; nc, sample not collected; *, result above threshold value; ±, plus or minus]
56 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program Table 12A. Uranium isotopes and radon-222 detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued [The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3I contains additional information about the analytes. Measured values less than the sample-specific critical level (ssLC) are reported as nondetections (—). GAMA well identi- fication number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: CSU, 1-sigma combined standard uncertainty; pCi/L, picocurie per liter; nc, sample not collected; *, result above threshold value; ±, plus or minus] GAMA well identification number Uranium-234 (pCi/L) (22610) Uranium-235 (pCi/L) (22620) Uranium-238 (pCi/L) (22603) Radon-222 (pCi/L) (82303) Threshold type1 MCL-CA MCL-CA MCL-CA Proposed MCL-US Threshold value 220 220 220 3300 (4,000) Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU4 TROCK-10 0.285 ± 0.033 0.013 0.031 ± 0.012 0.0089 0.136 ± 0.022 0.0074 870 ± 14 TROCK-11 0.061 ± 0.017 0.014

— 0.013 0.051 ± 0.014 0.0079 660 ± 14

TROCK-12 0.139 ± 0.021 0.0095 0.014 ± 0.011 0.0082 0.0203 ± 0.0085 0.0068 620 ± 13

TROCK-13 5.13 ± 0.25 0.016 0.042 ± 0.017 0.020 0.203 ± 0.042 0.016 420 ± 12

TTAHO-01 0.776 ± 0.051 0.011 0.023 ± 0.010 0.0077 0.265 ± 0.028 0.0090 350 ± 10

TTAHO-02 1.068 ± 0.061 0.0095 0.049 ± 0.014 0.0081 0.470 ± 0.040 0.0067 270 ± 9

TTAHO-03 0.035 ± 0.014 0.016

— 0.020

— 0.016 820 ± 14

TTAHO-04 0.030 ± 0.023 0.017

— 0.021

— 0.017 500 ± 11

TTAHO-05 0.026 ± 0.017 0.020

— 0.024 0.076 ± 0.026 0.020 1,590 ± 20

TTAHO-06 9.72 ± 0.35 0.029 0.367 ± 0.044 0.011 7.88 ± 0.29 0.026 1,530 ± 18

TTAHO-07 0.539 ± 0.042 0.012 0.0314 ± 0.0095 0.0073 0.515 ± 0.039 0.0060 1,280 ± 18

TTAHO-08 5.86 ± 0.21 0.017 0.203 ± 0.027 0.0079 4.63 ± 0.17 0.016 1,220 ± 16

TTAHO-09 0.536 ± 0.043 0.013 0.017 ± 0.011 0.0080 0.519 ± 0.043 0.0094 830 ± 14

TTAHO-10 0.734 ± 0.058 0.016 0.033 ± 0.014 0.011 0.640 ± 0.052 0.0091 2,340 ± 28

TTAHO-11 5.69 ± 0.20 0.017 0.183 ± 0.024 0.0069 2.74 ± 0.11 0.015 520 ± 12

TTAHO-12 0.087 ± 0.033 0.025

— 0.031 0.065 ± 0.033 0.025 640 ± 12

TTAHO-13 0.032 ± 0.016 0.021

— 0.011 0.024 ± 0.012 0.0094 1,930 ± 20

TTAHO-14 7.70 ± 0.26 0.022 0.283 ± 0.031 0.0077 6.97 ± 0.24 0.019 *10,800 ± 48
Tables 57

Table 12A. Uranium isotopes and radon-222 detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed. Table 3I contains additional information about the analytes. Measured values less than the sample-specific critical level (ssLC) are reported as nondetections (—). GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TROCKU, 

Hard Rock study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: CSU, 1-sigma combined standard uncertainty; pCi/L, picocurie per liter; nc, sample not collected; *, result above threshold value; ±, plus or minus]

GAMA well 

identification 

number

Uranium-234 

(pCi/L) 

(22610)

Uranium-235 

(pCi/L) 

(22620)

Uranium-238 

(pCi/L) 

(22603)

Radon-222 

(pCi/L) 

(82303)

Threshold type1 MCL-CA MCL-CA MCL-CA Proposed MCL-US

Threshold value

220 220 220 3300 (4,000)

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU4

Understanding wells

TMARTU-01 0.96 ± 0.13 0.033 0.051 ± 0.034 0.039 0.280 ± 0.070 0.033 1,440 ± 15

TROCKU-01 0.164 ± 0.025 0.0081 — 0.0099 0.098 ± 0.018 0.0081 820 ± 14

TROCKU-02 0.567 ± 0.081 0.026 — 0.031 0.156 ± 0.045 0.026 1,600 ± 19

TTAHOU-01 5.83 ± 0.20 0.020 0.248 ± 0.028 0.0070 4.72 ± 0.17 0.017 290 ± 11TTAHOU-02 0.474 ± 0.038 0.0091 0.020 ± 0.010 0.0078 0.405 ± 0.035 0.0091 1,100 ± 16

TTAHOU-03 7.74 ± 0.26 0.020 0.280 ± 0.031 0.0098 6.66 ± 0.22 0.017 *4,530 ± 31

TTAHOU-04 3.36 ± 0.14 0.017 0.151 ± 0.022 0.0086 2.88 ± 0.12 0.016 *4,220 ± 28

TTAHOU-05 *11.72 ± 0.40 0.036 *0.526 ± 0.052 0.011 *9.24 ± 0.33 0.031 *9,620 ± 49

TTAHOU-06 *21.10 ± 0.65 0.036 *0.827 ± 0.059 0.0082 *17.26 ± 0.54 0.033 1,610 ± 20

TTAHOU-07 1.369 ± 0.078 0.012 0.041 ± 0.015 0.0087 1.242 ± 0.072 0.012 *5,330 ± 35

TTAHOU-08 0.077 ± 0.017 0.0078 0.0122 ± 0.0080 0.0094 0.057 ± 0.014 0.0078 1,610 ± 18

1Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US 

exists.

2The MCL-US threshold for uranium is the sum of those for uranium-234, uranium-235, and uranium-238.3Two MCL-US have been proposed for radon-222. The proposed alternative MCL-US is in parentheses.4The 2-sigma combined standard uncertainties reported for radon-222 in the U.S. Geological Survey National Water Information System (NWIS) database have been divided by two and reported 

here as 1-sigma combined standard uncertainties for consistency with reporting of the other radiochemical constituents.
58 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

GAMA well 

identification 

number

Gross alpha 

particle activity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha 

particle activity, 

30-day count 

(pCi/L) 

(62639)

Gross beta 

particle activity, 

72-hour count 

(pCi/L) 

(62642)

Gross beta 

particle activity, 

30-day count 

(pCi/L) 

(62645)

Threshold 

type1 MCL-US MCL-US MCL-CA MCL-CA

Threshold 

value 15 15 50 50

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC

Grid wells

TMART-01 1.04 ± 0.71 0.77 — 1.1 3.19 ± 0.72 0.86 2.94 ± 0.55 0.66

TMART-06 — 0.89 — 1.2 1.75 ± 0.62 0.92 — 1.4

TROCK-13 — 4.2 — 3.8 11.5 ± 1.4 1.1 11.8 ± 1.4 0.97

TTAHO-02 1.21 ± 0.91 1.2 — 0.92 5.8 ± 1.1 1.4 4.77 ± 0.89 0.96

TTAHO-06 *25.9 ± 3.3 0.56 *26.1 ± 3.3 0.84 — 0.98 8.6 ± 1.2 0.85

TTAHO-10 2.98 ± 0.95 0.95 2.99 ± 0.81 0.67 2.75 ± 0.75 0.99 1.28 ± 0.56 0.84

TTAHO-11 2,*26.2 ± 4.6 3.5 8.9 ± 3.7 4.6 3

13.0 ± 1.6 1.1 13.8 ± 1.8 1.7

TTAHO-13 — 0.88 — 1.2 — 0.97 1.94 ± 0.87 1.3

Understanding wells

TMARTU-01 1.86 ± 0.82 0.82 — 1.0 5.17 ± 0.87 0.89 3.12 ± 0.72 0.90

TTAHOU-05 2,*36.1 ± 4.2 0.48 *32.4 ± 3.9 1.1 3

— 0.86 8.6 ± 1.4 1.4

Table 12B. Gross alpha and gross beta particle activities detected in samples collected for the Tahoe–Martis Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June-September 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from the 10 slow wells were analyzed (table 2). Table 3I contains additional information about the analytes. The reference nuclide for 

measurement of gross alpha particle activity is thorium-230 and the reference nuclide for measurement of gross beta particle activity is cesium-137. Measured 

values less than the sample-specific critical level (ssLC) are reported as nondetections (—). GAMA well identification number: TMART, Martis study area grid 

well; TROCK, Hard Rock study area grid well; TTAHO, Tahoe study area grid well; TMARTU, Martis study area understanding well; TTAHOU, Tahoe study 

area understanding well. Thresholds and threshold values as of June 1, 2008. Threshold type: MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: CSU, combined standard uncertainty; 

pCi/L, picocurie per liter; *, result above threshold value; ±, plus or minus]

1

 Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

 72-hour holding time exceeded by 1 day.

3

 72-hour holding time exceeded by 3 days.
Tables 59

GAMA well 

identification 

number

Radium-226 

(pCi/L) 

(09511)

Radium-228 

(pCi/L) 

(81366)

Threshold type1 MCL-US MCL-US

Threshold value 2

5 25

Result ± CSU ssLC Result ± CSU ssLC

Grid wells

TMART-01 ≤ 0.0147 ± 0.0080 0.011 — 0.19

TMART-06 ≤ 0.0187 ± 0.0090 0.012 — 0.17

TROCK-13 0.115 ± 0.016 0.013 — 0.17

TTAHO-02 ≤ 0.018 ± 0.010 0.014 — 0.18

TTAHO-06 ≤ 0.021 ± 0.011 0.016 — 0.18

TTAHO-10 ≤ 0.018 ± 0.012 0.017 — 0.24

TTAHO-11 0.251 ± 0.020 0.013 3.04 ± 0.15 0.19

TTAHO-13 0.046 ± 0.012 0.014 — 0.25

Understanding wells

TMARTU-01 ≤ 0.0171 ± 0.0090 0.013 — 0.21

TTAHOU-05 — 0.016 — 0.25

Table 12C. Radium isotopes detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June–September 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from the 10 slow wells were analyzed (table 2). Table 3I contains additional information about the analytes. Values less than the 

sample-specific critical level (ssLC) are reported as nondetections (—). Values less than the activities measured in field blanks (table A3A) are reported with a 

less than or equal to sign (≤). GAMA well identification number: TMART, Martis study area grid well; TROCK, Hard Rock study area grid well; TTAHO, 

Tahoe study area grid well; TMARTU, Martis study area understanding well; TTAHOU, Tahoe study area understanding well. Thresholds and threshold values 

as of June 1, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection 

Agency maximum contaminant level. Other abbreviations: CSU, combined standard uncertainty; pCi/L, picocurie per liter; ±, plus or minus]

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

The MCL-US threshold for radium is the sum of those for radium-226 and radium-228.
60 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Appendix

 This appendix includes discussions of the methods used 

to collect and analyze groundwater samples, the conventions 

used in reporting the resulting water-quality data, the methods 

used for quality assurance, and the results of quality-control 

assessments.

Sample Collection and Analysis

Groundwater samples were collected using standard and 

modified USGS protocols from the USGS NAWQA program 

(Koterba, and others, 1995) and the USGS National Field 

Manual (U.S. Geological Survey, variously dated), and protocols described by Weiss (1968), Shelton and others (2001), 

Ball and McClesky (2003a,b), and Wright and others (2005).

Samples were collected from three types of sites: production wells, monitoring wells, and springs (also called horizontal wells). Before sampling, each well was pumped continuously in order to purge at least three casing-volumes of water 

from the well (Wilde and others, 1999). For production wells, 

the existing pump on the well was used, and for monitoring 

wells, water was pumped using a portable, 2-inch diameter 

submersible pump (Grundfos RediFlo2 pump) attached to 

reels of approximately 300 feet of Teflon tubing. No pumping 

was required for springs. 

Groundwater samples were collected through Teflon 

tubing attached to a sampling point on the well (or spring) 

discharge pipe with brass and stainless-steel fittings. The 

sampling point was located as close as possible to the wellhead or point where the spring issued from the ground, and 

upstream of any water-storage tanks. The sampling point was 

also located upstream of well-head treatment systems (if any) 

for all sites except seven: TMART-02, -03, -09, and -14 and 

TROCK-12 and -13 had chlorination systems upstream of 

the sampling points that were turned off before sampling, and 

TTAHO-14 had a filter upstream of the sampling point. Most 

samples were collected inside an enclosed chamber located 

inside a mobile laboratory and connected to the sampling point 

by a 10- to 50-foot length of Teflon tubing (Lane and others, 

2003). At all of the springs and several of the wells, the mobile 

laboratory could not be driven within 50 feet of the sampling 

point. At these sites, samples were collected outdoors in a portable enclosed chamber connected to the sampling point by a 

1- to 2-foot length of Teflon tubing. All fittings and lengths of 

tubing were cleaned after each sample was collected (Wilde, 

2004).

For the field water-quality indicator measurements, 

groundwater was pumped through a flow-through chamber fitted with a multi-probe meter that simultaneously measured the 

field water-quality indicators—dissolved oxygen, temperature, 

pH, and specific conductance. Field measurements were made 

in accordance with protocols in the USGS National Field 

Manual (Radtke and others, 2005; Wilde and Radtke, 2005; 

Lewis, 2006; Wilde, 2006; Wilde and others, 2006). All sensors on the multi-probe meter were calibrated daily. Measured 

temperature, dissolved oxygen, pH, and specific conductance 

values were recorded at 5-minute intervals for at least 30 

minutes, and after these values remained stable for 20 minutes, samples to be analyzed in laboratories were collected. At 

monitoring wells, turbidity also was measured. Turbidity was 

measured in the mobile laboratory using a calibrated turbidity 

meter. Field measurements and instrument calibrations were 

recorded by hand on field record sheets and electronically in 

PCFF-GAMA, a software package designed by the USGS 

with support from the GAMA program. Analytical service 

requests also were managed by PCFF-GAMA. Information 

from PCFF-GAMA was uploaded directly into NWIS after 

samples were collected each week. 

For analyses requiring filtered water, groundwater was 

diverted through a 0.45-μm pore size vented capsule filter, a 

disk filter, or a baked glass-fiber filter, depending on the protocol for the analysis (Wilde and others, 1999; Wilde and others, 

2004). Before samples were collected, polyethylene sample 

bottles were pre-rinsed three times using deionized water, 

and then once with sample water before sample collection. 

Samples requiring acidification were acidified to a pH of 2 or 

less with the appropriate acids using ampoules of certified, 

traceable concentrated acids obtained from the USGS National 

Water Quality Laboratory (NWQL).

Samples collected to be analyzed for VOCs, pesticides, 

pharmaceuticals, nutrients, major ions, and trace elements 

were stored on ice, and shipped overnight in coolers with ice 

to the NWQL within three days of sample collection (samples 

were shipped daily whenever possible). Samples to be analyzed for radium isotopes, gross alpha and gross beta particle 

activities, uranium isotopes, and radon-222 were shipped 

overnight within two days of sample collection (samples were 

shipped daily whenever possible). Samples to be analyzed 

for perchlorate and NDMA were stored on ice and shipped in 

coolers with ice overnight at the end of each week. Samples to 

be analyzed for tritium, noble gases, chromium speciation, and 

stable isotopes of hydrogen and oxygen of water were shipped 

in batches after the last sample was collected in the study unit.
Appendix 61

Detailed sampling protocols for individual analyses and 

groups of constituents are described by Koterba and others (2005) and the USGS National Field Manual (Wilde and 

others, 1999; Wilde and others, 2004) and in the references 

for analytical methods listed in table A1. The brief descriptions given here are organized in the order that samples were 

collected at each well. Volatile organic compounds (VOC) 

and gasoline oxygenate and degradate samples were collected 

in 40-mL sample vials that were bottom-filled and purged 

with three vial volumes of sample water before being filled to 

eliminate entrainment of ambient air. Six normal (6 N) hydrochloric acid was added as a preservative to the VOC samples, 

but not to the gasoline oxygenate and degradate samples. 

Perchlorate samples to be analyzed at the Montgomery Watson 

Harza laboratory were collected in 125-mL polyethylene 

bottles. Tritium samples were collected by bottom filling two 

1-L polyethylene bottles with unfiltered groundwater after first 

overfilling the bottle with three volumes of water. Samples 

to be analyzed for stable isotopes of hydrogen and oxygen of 

water were collected in 60-mL clear glass bottles filled with 

unfiltered water, sealed with conical caps, and secured with 

electrical tape to prevent leakage and evaporation.

Samples to be analyzed for pesticides and pesticide 

degradation products, pharmaceutical compounds, and 

N-nitrosodimethylamine (NDMA) were collected in 1-L baked 

amber bottles. Pesticide and pharmaceutical samples were 

filtered through a 0.3-μm nominal pore-size glass fiber during 

collection, whereas the NDMA samples were filtered at the 

Montgomery Watson Harza and Weck laboratories before 

analysis. Each sample to be analyzed for perchlorate at the 

Weck laboratory was collected in a plastic bottle and then 

filtered in two or three 20-mL aliquots through a syringe-tip 

filter into a sterilized 125-mL bottle.

Groundwater samples to be analyzed for inorganic and 

radioactive constituents were filtered through a 0.45-μm 

pore-size Whatman capsule filter. Two 250-mL polyethylene 

bottles were filled for each sample to be analyzed for major 

and minor ions, trace elements, and total dissolved solids, one 

with filtered groundwater and the other with unfiltered groundwater (Wilde and others, 2004). The 250-mL filtered sample 

was then preserved with 7.5 N nitric acid. Samples to be used 

for field and laboratory alkalinity titrations were filtered into 

500-mL polyethylene bottles. Samples to be analyzed for 

species of arsenic and iron were filtered into 250-mL polyethylene bottles that were covered with tape to prevent light 

exposure, and preserved with 6 N hydrochloric acid. Samples 

to be analyzed for nutrients were filtered into 125-mL brown 

polyethylene bottles. Samples to be analyzed for radium 

isotopes, uranium isotopes, and gross alpha and gross beta particle activities were filtered into 1-L polyethylene bottles and 

acidified with nitric acid. Carbon isotope samples were filtered 

and bottom filled into two 500-mL glass bottles that were first 

overfilled with three bottle volumes of groundwater. These 

samples had no headspace and were sealed with a conical cap 

to prevent interaction between the sample and ambient air. 

Samples to be analyzed for chromium species, radon-222, 

and noble gases were collected from the sampling point on 

the well discharge pipe. Samples to be analyzed for chromium 

species were collected using a 10-mL syringe with an attached 

0.45-μm disk filter. After the syringe was thoroughly rinsed 

and filled with groundwater, 4 mL of groundwater was forced 

through the disk filter; the next 2 mL were slowly filtered 

into a small centrifuge vial for analysis of total chromium. A 

second small centrifuge vial was filled for analysis of hexavalent chromium, Cr(VI). A small cation exchange column was 

attached to the disk filter, and after conditioning the column 

with 2 mL of groundwater, 2 mL was collected in the second 

centrifuge vial. Both vials were preserved with 10 μL of 7.5 N 

nitric acid (Ball and McClesky, 2003a,b). 

To collect samples for analysis of radon-222, a stainless 

steel and Teflon valve assembly was attached to the sampling 

port at the well head (Wilde and others, 2004). The valve was 

partially closed to create back pressure, and a 10-mL sample 

was collected through a Teflon septum on the valve assembly 

using a glass syringe affixed with a stainless-steel needle. The 

sample was then injected into a 25-mL vial partially filled with 

scintillation mixture (mineral oil) and shaken. The vial was 

then placed in a cardboard tube in order to shield it from light 

during shipping. 

Samples for analysis of noble gases were collected in 

3/8-in copper tubes using reinforced nylon tubing connected to 

the hose bib at the wellhead. Groundwater was flushed through 

the tubing to dislodge bubbles before flow was restricted by a 

back pressure valve. Clamps on either side of the copper tube 

were then tightened, trapping a sample of groundwater to be 

analyzed for noble gases (Weiss, 1968). 

Alkalinity of filtered samples was measured in the mobile 

laboratory (“field” alkalinity) using Gran’s titration method 

(Gran, 1952; Stumm and Morgan, 1996; Rounds, 2006). Titration data were entered directly into PCFF-GAMA, and the 

concentrations of bicarbonate (HCO3

–

) and carbonate (CO3

2–

) 

were automatically calculated from the titration data using the 

advanced speciation method. Concentrations of HCO3

-

 and 

CO3

2–

 were also calculated from the laboratory alkalinity and 

pH measurements. Calculations were made in a spreadsheet 

using the advanced speciation method (http://or.water.usgs.

gov/alk/methods.html) with pK1 = 6.35, pK2 = 10.33, and 

pKW = 14. 
62 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Eleven laboratories did chemical and microbial analyses for this study (table A1), although most of the analyses 

were done at the NWQL or by laboratories contracted by the 

NWQL. The NWQL maintains a rigorous quality-assurance 

program (Pirkey and Glodt, 1998; Maloney, 2005). Laboratory 

quality-control samples, including method blanks, continuing 

calibration verification standards, standard reference samples, 

reagent spikes, external certified reference materials, and 

external blind proficiency samples, are analyzed regularly. 

Method detection limits are continuously tested and laboratory reporting levels updated accordingly. NWQL maintains 

National Environmental Laboratory Accreditation Program 

(NELAP) and other certifications (http://qadata.cr.usgs.gov/

nfqa). The Branch of Quality Systems within the USGS Office 

of Water Quality maintains independent oversight of quality assurance at the NWQL and laboratories contracted by 

the NWQL. In addition, the Branch of Quality Systems runs 

the National Field Quality Assurance program that includes 

annual testing of all USGS field personnel for proficiency in 

making field water-quality measurements (http://bqs.usgs.gov/

nfqa/). Results of analyses made at the NWQL or by laboratories contracted by the NWQL are uploaded from the laboratory 

directly into NWIS from the laboratory. Results of analyses 

made at other laboratories are compiled in a project Access 

(Microsoft, Redmond, Washington) database and uploaded 

from there into NWIS.

Data Reporting

The following section details the laboratory reporting 

conventions and the constituents that are determined by multiple methods or by multiple laboratories.

Reporting Limits

The USGS NWQL uses the laboratory reporting level 

(LRL) as a threshold for reporting analytical results. The 

LRL is set to reduce the chance of reporting a false negative 

(not detecting a compound when it is actually present in a 

sample) to less than 1 percent (Childress and others, 1999). 

The LRL is usually set at two times the long-term method 

detection level (LT-MDL). The LT-MDL is derived from the 

standard deviation for at least 24 MDL determinations made 

over an extended period of time. The method detection limit 

(MDL) is the minimum concentration of a substance that can 

be measured and reported with 99 percent confidence that the 

concentration is greater than zero (at the MDL there is less 

than 1 percent chance of a false positive) (Childress and others, 1999; U.S. Environmental Protection Agency, 2002). The 

USGS NWQL updates LRL values regularly and the values 

listed in this report were in effect when groundwater samples 

from the Tahoe–Martis study unit (June–October 2007) were 

analyzed.

Concentrations between the LRL and the LT-MDL are 

reported as estimated concentrations (designated with an “E” 

before the values in the tables and text). In rare cases, concentrations above the LRL may be reported as E-coded values. 

These cases may occur if the concentration was outside the 

range of the calibration standards, if the sample was diluted 

before analysis, or if the result did not meet all laboratory 

quality-control criteria (Childress and others, 1999).

Some constituents in this study are reported using minimum reporting levels (MRL) or method uncertainties. The 

MRL is the smallest measurable concentration of a constituent 

that may be reliably reported using a given analytical method 

(Timme, 1995). The method uncertainty generally indicates 

the precision of a particular analytical measurement; it gives a 

range of values wherein the true value will be found. 

Results for most constituents are presented using the LRL 

or MRL values provided by the analyzing laboratories. Results 

for some constituents are presented using study reporting 

levels (SRL) derived from assessing data from quality-control 

samples associated with groundwater samples collected as 

part of the GAMA project. The SRLs for trace elements were 

determined by statistical assessment of results from the field 

blanks collected in the first 20 GAMA study units (May 2004 

through January 2008) (L.D. Olsen and M.S. Fram, U.S. 

Geological Survey, unpub. data, 2008). The assessment used 

order statistics and binomial probabilities to construct an upper 

confidence limit (Hahn and Meeker, 1991) for the maximum 

concentration of constituents potentially introduced while 

groundwater samples were collected, handled, transported, and 

analyzed. The resulting SRLs for trace elements were set at 

concentrations representing the upper 90 percent confidence 

limit for the 90th percentile of the 86 field blanks used in the 

assessment. 

The SRLs for major and minor ions, nutrients, species of 

arsenic, iron, and chromium, and radioactive constituents were 

determined by assessment of results from field blanks collected in the Tahoe–Martis study unit. The maximum concentration of a constituent potentially introduced while groundwater samples were collected, handled, transported, and analyzed 

was defined as the maximum concentration of the constituent 

measured in blanks collected in the Tahoe–Martis study unit.

For most constituents, this maximum concentration was 

below the LRL or MRL for the constituent. Data for such 

constituents are reported with the LRL or MRL. For some 

constituents, this maximum concentration was greater than the 

LRL or MRL, and therefore was defined as the SRL. Detections of those constituents reported by the laboratory with 

concentrations greater than the LRL or MDL but less than the 

SRL are given in tables 7–10 and 12 with a less-than-or-equalto (≤) sign preceding the reported value.
Appendix 63

The methods used to analyze radiochemical constituents (gross alpha particle activity, gross beta particle activity, 

radium isotopes, and uranium isotopes) measure activities 

by using counting techniques (table A1). The reporting limits 

for radiochemical constituents are based on sample-specific 

critical levels (ssLC) (McCurdy and others, 2008). The critical 

level is analogous to the LT-MDL used for reporting analytical 

results for organic and non-radioactive inorganic constituents. 

In this report, the critical level is defined as the minimum 

measured activity that indicates a positive detection of the 

radionuclide in the sample with less than a 5-percent probability of a false positive detection. The critical level depends 

on instrument background, counting times for the sample and 

background, and the characteristics of the instrument being 

used and the nuclide being measured. Sample-specific critical levels are used because the critical level also depends on 

sample size and sample yield during analytical processing. An 

ssLC is calculated for each sample, and the measured activity in the sample is compared to the ssLC associated with that 

sample. Measured activities less than the ssLC are reported as 

nondetections. 

The analytical uncertainties associated with measuring 

activities are sensitive to sample-specific parameters also, 

including sample size, sample yield during analytical processing, and time elapsed between sample collection and various 

steps in the analytical procedure, as well as parameters associated with the instrumentation. Therefore, measured activities 

of radioactive constituents are reported with sample-specific 

uncertainties. Activities of uranium isotopes, radium isotopes, 

and gross alpha and gross beta particle activities are reported 

with sample-specific 1-sigma combined standard uncertainties 

(CSU). Radon activities are reported with 2-sigma combined 

standard uncertainties in the USGS NWIS database and are 

reported here with 1-sigma combined standard uncertainties 

to be consistent with reporting of the other radiochemical 

constituents.

Notation

Stable isotopic compositions of oxygen, hydrogen, and 

carbon are reported as relative isotope ratios in units of per mil 

using the standard delta notation (Coplen and others, 2002):

 iE

R

R

i

= − 



 



 sample

reference

 per mil

where 

is the at

1 1 000 i ,

omic mass of the heavier isotope of 

the element, 

E is the element (O for oxygen, C for carbon, 

or H for hydrogen), 

sa R mple is the ratio of the abundance of the heavier 

isotope of the element ( O, C, or H) to 

that of the lighter isot

18 213

ope of the element 

( O, C, or H) in the sample and, 16 12 1

Rreference is the ratio of the abundance of the heavier 

isotope of the element to that of the lighter isotope

of the element in the reference material.

The reference material for oxygen and hydrogen is 

Vienna Standard Mean Ocean Water (VSMOW), which is 

assigned δ18O and δ2H values of 0 per mil (note than δ2H is 

sometimes referred to as δD because the common name of 

the heavier isotope of hydrogen, hydrogen-2, is deuterium). 

The reference material for carbon is Vienna Peedee Belemnite 

(VPDB), which is assigned a δ13C value of 0 per mil. Positive 

values indicate enrichment of the heavier isotope and negative 

values indicate depletion of the heavier isotope, compared to 

the ratios observed in the standard reference material.

Constituents on Multiple Analytical Schedules

Fourteen constituents targeted in this study were measured by more than one analytical schedule or more than 

one laboratory (table A2). The preferred methods for these 

constituents were selected on the basis of the procedure 

recommended by the NWQL (http://wwwnwql.cr.usgs.gov/

USGS/Preferred_method_selection_procedure.html). Methods 

with full approval are preferred over those with provisional 

approval and approved methods are favored over research 

methods. The method having greater accuracy and precision 

and lower LRLs for the overlapping constituents is usually 

preferred. However, the method having higher LRLs may be 

selected as the preferred method to provide consistency with 

the historical data analyzed by the same method.

For the five constituents on NWQL Schedules 2020 

(VOCs; table 3A) and 4024 (gasoline oxygenates; table 3B), 

the preferred method was Schedule 2020 to provide historical consistency (all samples collected for the GAMA Priority 

Basin Project are analyzed using Schedule 2020). Only the 

results from the preferred method are reported.
64 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

For arsenic, chromium, and iron concentrations, the 

approved method, Schedule 1948, used by the NWQL is 

preferred over the research methods used by the USGS Trace 

Metal Laboratory. The concentrations measured by the Trace 

Metal Laboratory are used only to calculate ratios of redox 

species for each element: As(V)

As(III) for arsenic, for Cr(VI)

Cr(III)

chromium, and Fe(III)

Fe(II) for iron; for example,

Fe(III)

Fe(II)

Fe(T) - Fe(II)

Fe(II)

where 

Fe(T) is the total i

=

ron concentration (measured)

Fe(II) is the concentration of ferrous iron (measured), and

Fe(III) is the concentration of ferric iron (calculated).

Constituents Analyzed in the Field and the 

Laboratory

The field water-quality indicators—pH, specific conductance, and alkalinity—were measured in the field and at the 

NWQL. The field measurements are the preferred method for 

all three constituents, although results from field and laboratory measurements were reported. The field and laboratory 

results were compared statistically to assess potential bias in 

datasets consisting of field values for some samples and 

laboratory values for other samples.

The field and laboratory data were compared using the 

Wilcoxon signed-rank test, a nonparametric statistical test that 

is analogous to the parametric statistical test the paired t-test 

(Helsel and Hirsch, 2002). A nonparametric test was used 

because the data were not normally distributed. The Wilcoxon 

signed-rank test evaluates the null hypothesis that the median 

of the paired differences between the two data sets is zero. 

Results are reported as the probability, P, of obtaining the 

observed distribution of data, or one even less likely, when the 

null hypothesis is true. Therefore, a P value of 0.01 indicates 

99 percent confidence that the two data sets are different. 

Specific conductance in all 52 samples was measured 

in both the field and the laboratory. The median difference 

between field and laboratory measurements on the same 

sample was 4 percent higher values for the laboratory result 

(P = 0.002). The reason for this discrepancy is unknown. The 

values for specific conductance measured in the field were 

used to describe and assess groundwater quality because field 

values were available for all samples, and field conditions are 

considered more representative of groundwater conditions 

(Hem, 1985).

 Both laboratory and field pH measurements were made 

for all 52 samples, and the two data sets were systematically 

different (P < 0.001). Laboratory pH values ranged from 

0.3 pH units lower to 1.6 pH units higher than field pH values 

for the same sample; the median difference was 0.2 pH units 

higher. The discrepancy may be due to difficulties inherent in measuring pH in natural waters, particularly in waters 

with low concentrations of dissolved solids. It is difficult to 

measure pH in water samples having a specific conductance 

less than 100 μS/cm because of the high diffusion potential 

between the water sample and the reference electrolyte in the 

pH probe and the high resistance of the water sample to the 

propagation of electrical current (Galster, 1991). There were 

12 groundwater samples having a specific conductance less 

than 100 μS/cm, and the median difference between laboratory and field pH values for the same sample was laboratory 

value higher by 0.48 pH unit. In comparison, there were 

40 groundwater samples having a specific conductance greater 

than 100 μS/cm, and the median difference between laboratory 

and field pH values for the same sample was laboratory value 

higher by only 0.15 pH units. The conditions of the field pH 

measurements are more likely to give an accurate pH reading 

than the conditions of the laboratory pH measurements, particularly because of the use of a flow-through chamber and the 

longer contact time between the pH probe and groundwater in 

the field. Because most of the groundwater samples that have a 

specific conductance less than 100 μS/cm also have pH values 

less than 7, insufficient contact time would result in pH values 

biased high (towards the pH of the buffer solution in which the 

probe is stored when not in use in the laboratory). In addition, 

pH values of groundwater samples with low dissolved solids 

content will generally increase if the samples are inadvertently 

contaminated by contact with pH buffer solutions or other 

sources of ions (Galster, 1991). 

The increase in pH of the groundwater samples between 

field and laboratory measurements also may be explained by 

equilibration of the sample with the atmosphere after collection. The partial pressure of CO2

 in groundwater is often 

greater than the atmospheric partial pressure (Appelo and 

Postma, 2005), thus CO2 degasses from the groundwater when 

it is brought in contact with the atmosphere. CO2 loss results 

in increased pH. The field values for pH were used to describe 

and assess groundwater quality because field values are available for all samples, and field values are preferred because 

field conditions are considered more representative of groundwater conditions (Hem, 1985) and because analytical issues 

may introduce bias in the laboratory values, as discussed 

above. 

Alkalinities of 10 samples were measured in the field and 

in the laboratory. The median difference between the laboratory and field measurements on the same sample was 11 percent higher alkalinity measured in the laboratory (P < 0.002). 

This 11 percent difference is greater than the error associated 

with replicate alkalinity measurements (Rounds, 2006). Alkalinity does not change with loss or gain of CO2

 from the water 

(Stumm and Morgan, 1996); thus, the increase in alkalinity 

was not likely caused by equilibration between the sample 

and the atmosphere during the time between the field and the 

laboratory measurements. Part of the discrepancy may be due 

to the difference between the Gran’s titration method used in 

the field and the fixed-endpoint (pH = 4.5) titration used in the 
Appendix 65

laboratory. The fixed-endpoint method systematically yields 

higher alkalinity values, particularly for samples containing 

low concentrations of dissolved inorganic carbon, because the 

titration equivalence point shifts to higher pH values as the 

dissolved inorganic carbon content of the sample decreases. 

For the ten samples in which alkalinity was measured in both 

the field and the laboratory, the median cation-anion imbalance was –1.3 percent if the laboratory alkalinity values were 

used to calculate bicarbonate and carbonate concentrations and 

+3.7 percent if the field alkalinity values were used. Because 

the laboratory alkalinity values usually yielded better cationanion balances than the field alkalinity values, the laboratory 

alkalinity values were used in the assessments of groundwater 

quality.

Quality Assurance

The purpose of quality assurance is to identify which data 

best represent environmental conditions and which may have 

been affected by contamination or bias during sample collection, processing, storage, transportation, and (or) laboratory 

analysis. Four types of quality-control (QC) tests were used in 

this study: blanks were collected to assess contamination during sample collection, handling or analysis; replicate samples 

were collected to assess reproducibility; matrix spike tests 

were done to assess accuracy of laboratory analytical methods; 

and surrogate compounds were added to samples analyzed 

for organic constituents to assess bias of laboratory analytical 

methods. 

In this report, detections of organic constituents in 

groundwater samples that may have resulted from contamination during sample collection, handling, or analysis were 

flagged with “V” remark codes in the results tables (tables 5, 

6) and were not considered detections for calculations of 

detection frequencies in water-quality assessments. Detections 

of inorganic constituents in groundwater samples that may 

have resulted from contamination during sample collection, 

handling, or analysis were flagged to indicate that the amount 

of potential contamination may have been sufficient to give 

a false positive relative to the stated reporting level. Because 

of the possible contamination, the actual concentration in the 

groundwater sample may be less than or equal to (≤) the measured concentration. The evaluation of QC data presented in 

this report was based on results for QC samples collected for 

the Tahoe–Martis study unit and on results for QC samples for 

the 20 GAMA study units sampled from May 2004 through 

January 2008. 

The quality assurance protocols used for this study 

followed the protocols used by the USGS NAWQA program (Koterba and others, 1995) and described in the USGS 

National Field Manual (U.S. Geological Survey, variously 

dated). The quality-assurance plan followed by the NWQL, 

the primary laboratory used to analyze samples for this study, 

is described by Maloney (2005) and Pirkey and Glodt (1998). 

Blanks

The primary purposes of collecting blanks are to evaluate the magnitude of potential contamination of samples by 

constituents of interest during sample collection, handling, 

or analysis, and to identify and mitigate sources of this 

contamination. 

Blank Collection and Analysis

Blanks were collected using blank water certified by the 

NWQL to contain less than the LRL or MRL of the constituents investigated in the study (http://wwwnwql.cr.usgs.gov/

USGS/OBW/obw.html). Nitrogen-purged, organic-free blank 

water was used for field blanks of organic constituents, and 

inorganic-free blank water was used for field blanks of other 

constituents. Two types of blanks were collected: source-solution and field blanks. Source-solution blanks were collected 

to assess potential contamination of samples during transport 

and analysis, and potential contamination of the certified blank 

water obtained from the USGS NWQL. Field blanks were 

collected to assess potential contamination of samples during 

collection, processing, transport, and analysis. 

For Tahoe–Martis, blanks were collected at 12 percent 

of the wells sampled. Field blanks were analyzed for VOCs; 

gasoline oxygenates and degradates; pesticides; pharmaceuticals; perchlorate; NDMA; nutrients; major and minor ions; 

trace elements; iron, arsenic, and chromium speciation; and 

radioactive constituents (table A3A). Blank water certified to 

be free of tritium and noble gases was not available, thus field 

blanks were not collected and analyzed for these constituents. 

The concept of blank samples does not apply to analyses of 

stable isotope ratios because the constituents (oxygen and 

hydrogen in water, and carbon in dissolved inorganic carbon) 

are in all samples.

Source-solution blanks were collected at the sampling 

site by pouring blank water directly into sample containers 

that were preserved, stored, shipped, and analyzed in the same 

manner as the groundwater samples. For field blanks, blank 

water was either pumped or poured through the sampling 

equipment (fittings and tubing) used to collect groundwater, 

then processed, transported, and analyzed using the same protocols used for the groundwater samples. Eight to twelve liters 

of blank water were pumped or poured through the sampling 

equipment before the field blank was collected.
66 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Assessment of Blanks

Contamination in blanks may originate from several 

different types of sources that require different strategies to 

assess potential contamination of groundwater samples during 

sample collection, handling, or analysis. Four primary modes 

of contamination are assessed in the event of detections in 

field-blanks or unusual results in groundwater samples: (1) 

impurities in the water used to collect the blanks, (2) contamination during sample collection and handling from a known 

source or condition present at the field site, (3) carry-over of 

material from one sample to the next sample collected with 

the same sampling equipment, and (4) systematic and random contamination from field and laboratory equipment and 

processes. The fourth source of contamination (systematic and 

random) was addressed using a larger set of field blank results 

from multiple studies, in addition to the results from field 

blanks collected during the Tahoe–Martis study. The development of this approach and its methods are described by L.D. 

Olsen and M.S. Fram (U.S. Geological Survey, unpub. data, 

2008)

The first potential mode evaluated was the presence of 

impurities in the blank water. Because the blanks were collected using blank water certified by the NWQL to contain 

less than the LRL or MRL of the constituents investigated in 

the study, the blank water itself is very rarely the source of 

constituents detected in field blanks. However, blank water 

is sometimes used before the certification process has been 

completed; thus, the certificates of analysis must always be 

checked.

The second potential mode evaluated was contamination from identifiable, known sources at a specific field site. 

Contamination from specific sources may produce distinctive 

patterns of detections (particularly of VOC constituents) in 

field blanks and groundwater samples. Substances that may be 

encountered at the field site, such as lubricants (for example, 

WD-40), cements used on PVC-piping, exhaust fumes from 

pump engines, and the methanol used to clean sample lines, 

contain recognizable associations of VOC constituents. For 

example, cements used on PVC-piping are composed primarily of tetrahydrofuran, acetone, methyl ethyl ketone (MEK), 

and cyclohexanone (not analyzed in this study). However, 

detecting these recognizable associations of VOC constituents 

in groundwater samples does not necessarily indicate contamination during sample collection because these VOC constituents may also occur together in groundwater.

If a recognizable association of VOC constituents was 

detected in a field blank or in a groundwater sample, the field 

notes and photographs from the site at which the sample was 

collected were examined for conditions that may have caused 

the field blank or the groundwater sample to be contaminated. 

If the constituents were present in the field blank and the 

groundwater sample from the same site at similar concentrations and the field notes or photographs indicated that the 

probable contaminant source was present, the detections of 

those constituents in the groundwater sample were V-coded, 

and all other groundwater samples collected at sites where 

the same condition may have occurred were considered for 

V-coding. If the constituents were detected in a groundwater 

sample and not the in associated field blank, or a in groundwater sample from a site where no blanks were collected, and the 

field notes or photographs indicated conditions that may have 

resulted in contamination of the groundwater sample during 

sample collection, the data were considered for V-coding. If 

no conditions that may have resulted in contamination of the 

groundwater sample during sample collection were identified 

in the field notes or photographs, V-codes were not applied on 

this basis. 

The third potential mode of contamination evaluated was 

“carry-over” from the previous groundwater sample or field 

blank collected with the same equipment. Carry-over between 

samples is very rare because the procedures used to clean the 

equipment after each use have been developed and extensively tested to assure that carry-over does not occur. Potential 

carry-over was evaluated using time-series analysis to look for 

patterns suggestive of carry-over of constituents from a sample 

with high concentrations to the next groundwater sample or 

field blank collected with the same equipment. If nondetections were reported for a constituent in field blanks or groundwater samples collected after groundwater samples containing 

high concentrations of the constituent, then carry-over was 

ruled out as a mode of contamination for that constituent. 

The fourth potential mode of contamination evaluated was random or systematic contamination from field or 

laboratory equipment or processes. All detections in field 

blanks which could not be accounted for by impurities in the 

source-solution water, specific known conditions at field sites, 

or carry-over between samples were evaluated for random 

contamination. Random contamination in field and laboratory 

processes has an equal chance of affecting each groundwater 

sample thus, strategies for flagging detections of constituents 

subject to random contamination in field and laboratory processes must be applied to all groundwater samples. 

Different notation was used for flagging results for 

organic and inorganic constituents that may have been affected 

by contamination during sample collection, handling, or analysis. Inorganic constituents are naturally present in groundwater, and the concerns about inorganic constituents usually are 

related to concentration, rather than detection (presence or 

absence). In contrast, concerns about organic constituents usually are related to both detection and concentration. Therefore, 

different schema are used for assessing and flagging data for 

organic and inorganic constituents.
Appendix 67

Results for organic constituents that may have been 

affected by contamination during sample collection, handling, or analysis were flagged with V-codes. The purpose 

of V-coding was to flag detections that have a greater than 

acceptable probability of being false-positive detections. A 

false-positive detection of a constituent is an apparent detection that is caused by contamination during the sample collection, handling, or analysis of a groundwater sample that would 

otherwise not have a detection for of that constituent. Results 

labeled with V-codes were not considered to be detections of 

the constituent for this study and were not included in calculations of detection frequencies for organic constituents.

The V-coding level was defined as the highest concentration of the constituent detected in a field blank plus the LTMDL (equal to one-half the LRL) for that constituent. The following example illustrates why the V-coding level is defined 

in this way. In this example, the LT-MDL for the constituent is 

0.10 μg/L, the true concentration in the groundwater sample 

is 0.05 μg/L, and the highest concentration detected in a field 

blank is 0.20 μg/L. It is assumed that the highest concentration 

measured in a field blank represents the maximum amount of 

contamination that groundwater samples may receive during 

collection, handling, transport, or analysis. If the groundwater 

sample is not affected by contamination during collection, 

handling, transport, or analysis, the measured concentration 

will be reported as a nondetection (0.05 μg/L is less than the 

LT-MDL of 0.10 μg/L). If the maximum amount of contamination (0.20 μg/L) occurs, then the measured concentration will 

be 0.25 μg/L, which is reported as a detection of the constituent. Therefore, by setting the V-coding level at 0.30 μg/L (the 

LT-MDL of 0.10 μg/L plus the potential maximum amount of 

contamination of 0.20 μg/L), detections that might be falsepositive detections are removed from of the dataset. 

Results for inorganic constituents that may have been 

affected by contamination during sample collection, handling, 

transport, or analysis were flagged with a less than or equal to 

symbol (≤). The ≤ symbol means that the true concentration 

of the constituent in the groundwater sample is less than or 

equal to the measured concentration (including the possibility 

that it may be less than the LT-MDL and therefore a nondetection). For trace elements, the concentration cutoff, hereinafter 

referred to as the study reporting limit (SRL), for assigning 

the ≤ symbol was determined from a statistical assessment of 

results for 86 field blanks collected between May 2004 and 

January 2008 (L.D. Olsen and M.S. Fram, U.S. Geological 

Survey, unpub. data, 2008). For all other inorganic constituents, the SRL for assigning the ≤ symbol was determined from 

assessing the field blanks collected at Tahoe–Martis sites only. 

The SRL was defined as equaling the highest concentration 

measured in the six field blanks collected at Tahoe–Martis 

sites (field blanks were collected at 12 percent of the wells 

sampled).

Replicates

Sequential replicate samples were collected to assess the 

precision of the water-quality data. Estimates of data precision 

are needed to assess whether differences between concentrations in samples are due to differences in groundwater quality 

or to variability that may result from collecting, processing 

and analyzing the samples.

Two methods for measuring variability were needed to 

adequately assess precision over the broad range of measured 

concentrations of most constituents. The variability between 

measured concentrations in the pairs of sequential replicate 

samples was represented by the standard deviation (SD) for 

low concentrations and by relative standard deviation (RSD) 

for high concentrations (Anderson, 1987; Mueller and Titus, 

2005). The RSD is defined as the SD divided by the mean 

concentration for each replicate pair of samples, expressed as 

a percentage. The boundary between concentrations for which 

variability is assessed with SD and concentrations for which 

variability is assessed with RSD was defined as 5 times the 

LRL for each constituent. 

 For this study, acceptable precision for replicate sample 

pairs is defined as follows:

• For concentrations less than 5 times the LRL 

(< 5 LRL), an SD of less than 1⁄2 LRL is acceptable

• For concentrations greater than (or equal to) 5 times 

the LRL (> 5 LRL), an RSD of less than 10 percent 

is acceptable. For comparison, an RSD of 10 percent 

is equivalent to a relative percent difference (RPD) of 

14 percent. 

• For activities of radiochemical constituents, the presence of overlap between the results (value ± 1-sigma 

CSU) is acceptable

If results from replicate sample pairs indicate that precision is unacceptable for a constituent, and no specific reason 

can be identified, this greater variability must be considered 

when the data are used for the purposes of comparison. If 

measured concentrations are slightly above a water-quality 

threshold, then actual concentrations could be slightly below 

that threshold. Similarly, if measured concentrations are 

slightly below a water-quality threshold, then actual concentrations could be slightly above. Also, if a constituent has 

high variability in replicate sample pairs, a larger difference 

between concentrations measured in two samples is required 

to conclude that the two samples have significantly different 

concentrations. 

For organic and inorganic constituents (except for radiochemical constituents), if both values for a replicate sample 

pair were reported as detections, the SD was calculated if the 

mean concentration was <5 LRL for the constituent or the 

RSD was calculated if the mean concentration was ≥5 LRL for 

the constituent. If both values were reported as nondetections, 

the variability was set to zero by definition. Cases other than 

two detections or two nondetections were treated as follows:
68 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

• For organic constituents, if one or both values were 

assigned a V-code, neither SD nor RSD was calculated. 

A V-code indicates that the constituent was detected in 

blanks and was excluded from the dataset of groundwater quality results. The data might not represent the 

concentration of the constituent in the groundwater 

sample.

• For organic and inorganic constituents, if one value 

was reported as a nondetection, and the other value 

was reported as a detection below the LRL, a value 

of zero was substituted for the nondetection and the 

SD calculated. Substituting zero for the nondetection 

yields the maximum estimate of variability for the 

replicate pair. 

• For inorganic constituents, if one value for a sample 

pair was reported as a nondetection and the other value 

was reported as a ≤-coded value less than the SRL, 

or if both values were reported as ≤-coded values less 

than the SRL, neither SD nor RSD was calculated, 

because the values may be analytically identical. The 

≤-code indicates that the value is a maximum potential concentration, and that concentration may be low 

enough to be reported as a nondetection. 

• For organic and inorganic constituents, if one value 

was reported as a nondetection and the other value was 

reported as a detection greater than the LRL, the 

variability for the pair was considered unacceptable.

Matrix Spikes

Adding a known concentration of a constituent (‘spike’) 

to a replicate environmental sample enables the analyzing 

laboratory to determine the effect of the matrix, in this case 

groundwater, on the analytical technique used to measure the 

constituent. The known compounds added in matrix spikes 

are the same as those being analyzed in the method. This 

enables an analysis of matrix interferences on a compound-bycompound basis. Matrix spikes were added at the laboratory 

doing the analysis. Low matrix-spike recovery may indicate 

that the compound might not be detected in some samples if it 

was present at very low concentrations. Low and high matrixspike recoveries may be a concern if the concentration of a 

compound in a groundwater sample is close to the MCL: a 

low recovery could falsely result in a measured concentration 

below the MCL, whereas a high recovery could falsely result 

in a measured concentration above the MCL.

The GAMA program defined the data quality objective 

for acceptable matrix-spike recoveries as 70 to 130 percent. 

Constituents with matrix-spike recoveries outside of this range 

were flagged as having unacceptable recoveries in table 3C 

(none of the constituents listed in tables 3A,B,E had unacceptable matrix-spike recoveries). For many constituents, 

an acceptable range of 70 to 130 percent for matrix spike 

recovery was more restrictive than the acceptable control limits for laboratory “set” spike recoveries. Laboratory set spikes 

are aliquots of laboratory blank water to which the same spike 

solution used for the matrix spikes has been added. One set 

spike is analyzed with each set of samples. Acceptable control 

limits for set spikes are defined relative to the long-term variability in recovery. For example, for many NWQL schedules 

acceptable set spike recovery is within plus or minus three 

F-pseudosigma of the median recovery for at least 30 set 

spikes (Conner and others, 1998; Rose and Sandstrom, 2003). 

For NWQL schedule 2080, acceptable set spike recovery is 

within plus or minus two standard deviations of the long-term 

mean recovery (Furlong and others, 2008). 

Matrix spike recovery tests were done for VOCs, gasoline oxygenates and degradates, pesticides, pharmaceuticals, 

and NDMA because the analytical methods for these constituents are chromatographic methods that may be susceptible 

to matrix interferences. Replicate samples for matrix-spike 

recovery tests were collected at 12 percent of the wells 

sampled.

Surrogates

Surrogate compounds are added to environmental samples in the laboratory before analysis in order to evaluate the 

recovery of similar constituents. Surrogate compounds were 

added in the laboratory to groundwater and quality-control 

samples that were analyzed for VOCs, gasoline oxygenates 

and degradates, pesticides, pharmaceuticals, and wastewaterindicators by the NWQL, and for NDMA by the MWH laboratory. Most of the surrogate compounds are deuterated analogs 

of compounds being analyzed. For example, the surrogate 

toluene-d8 used for the VOC analytical method has the same 

chemical structure as toluene, except that the eight hydrogen-1 atoms on the molecule have been replaced by deuterium 

(hydrogen-2). Toluene-d8 and toluene behave very similarly 

in the analytical procedure, but the small mass difference 

between the two results in slightly different chromatographic 

retention times thus the use of a toluene-d8 surrogate does 

not interfere with the analysis of toluene (Grob, 1995). Only 

0.015 percent of hydrogen atoms are deuterium (Firestone 

and others, 1996) thus deuterated compounds like toluened8 do not exist naturally and are not found in environmental 

samples. Surrogates are used to identify general problems that 

may arise during sample analysis that could affect the analysis 

results for all compounds in that sample. Potential problems 

include matrix interferences (such as high levels of dissolved 

organic carbon) that produce a positive bias, or incomplete 

laboratory recovery (possibly because of improper maintenance and calibration of analytical equipment) that produces 

a negative bias. A 70- to 130-percent recovery of surrogates 

is generally considered acceptable; values outside this range 

indicate possible problems with the processing and analyzing samples (Connor and others, 1998; Sandstrom and others, 

2001).
Appendix 69

Quality-Control Results

Detections in Field and Source-Solution Blanks

Six field blanks and three source-solution blanks 

were collected for analysis of VOCs, and three VOCs were 

detected: toluene, 1,2,4-trimethylbenzene, and methyl ethyl 

ketone (MEK). Toluene was detected in two field blanks at 

a concentration of E0.02 μg/L. Concentrations of toluene 

between E0.01 μg/L and E0.08 μg/L were detected in approximately 40 percent of the field and source-solution blanks in 

other study units (Wright and others, 2005; Bennett and others, 

2006; Kulongoski and others, 2006; Fram and Belitz, 2007; 

Kulongoski and Belitz, 2007; Dawson and others, 2008; Ferrari and others, 2008; and Landon and Belitz, 2008). Because 

the certificates of analysis stated that no toluene was detected 

in the lots of nitrogen-purged, organic-free blank water used 

when the Tahoe–Martis samples were collected, the source 

blank water was not considered to be the source of the contamination. The source of the toluene is not known. Because 

toluene is detected frequently in both source-solution and field 

blanks, all toluene detections in groundwater samples collected in GAMA study units are subject to V-coding at a level 

based on the concentrations detected in the blanks. The concentration of toluene detected in two Tahoe–Martis groundwater samples was E0.02 μg/L in two groundwater samples; 

both of these detections were V-coded and excluded from the 

dataset of groundwater quality results (tables 5, A3).

1,2,4-Trimethylbenzene was detected in 3 of the 6 field 

blanks at concentrations of E0.05, E0.05, and 0.12 μg/L, and 

in 1 source-solution blank at a concentration of E0.03 μg/L. 

Because the certificates of analysis stated that no 

1,2,4-trimethylbenzene was detected in the lots of nitrogenpurged, organic-free blank water used when the Tahoe–Martis 

samples were collected, the source blank water was not considered to be the source of the contamination. 1,2,4-Trimethylbenzene was detected in 20 of the 52 groundwater samples 

at concentrations ranging from E0.02 to 0.13 μg/L (median 

E0.05 μg/L). The frequency and the concentrations at which 

1,2,4-trimethylbenzene was detected in both the groundwater 

samples and the blanks suggest that groundwater samples and 

blanks were randomly contaminated with 1,2,4-trimethylbenzene from an unknown source while being collected, handled, 

transported, or analyzed. All detections of 1,2,4-trimethylbenzene in groundwater samples were V-coded and excluded from 

the dataset of groundwater quality results (tables 5 and A3).

The pattern of VOC detections observed in one of the 

field blanks led to an unusual opportunity to demonstrate the 

importance of the rigorous procedures for cleaning equipment after samples are collected. Three vials are filled in the 

field for each VOC sample or blank, and the laboratory (the 

NWQL) randomly selects one to be analyzed for VOCs and 

reserves the other two for reruns that may be necessary if there 

are problems with the analysis of the first vial or if the project 

(GAMA) requests a rerun to verify a detection. Under normal circumstances, the three vials collected for a sample or a 

blank would yield the same results. Highly unusual conditions 

occurred when one of the field blanks was being collected 

and resulted in the three vials having markedly different VOC 

results.

The normal procedure for cleaning equipment after collecting a sample entails flushing the equipment with soapy 

water followed by rinsing it with clean water, then flushing it 

with methanol followed by rinsing it with clean water. In the 

field notes for the site at which the unusual field blank was 

collected, the field crew recorded that they thought they might 

not have rinsed the peristaltic pump used to pump the blank 

water from the source bottles through the sampling equipment 

and into the sample vials with clean water after the methanol 

flush. The three VOC vials are the first sample containers to 

be filled during sample collection, and therefore the VOC 

results would be the most affected by any contaminants from 

the methanol. The collection order is not marked on the three 

vials. The NWQL randomly selects one of the three vials collected for analysis and only uses the other vials if the analysis 

of the first vial was not successful. 

The NWQL notified us immediately upon noticing a high 

number of VOC detections and an unusual chromatogram for 

our field blank (even before releasing the data to us). Information in the field notes led us to suspect that residual methanol 

may have been the source, and we requested that the remaining two vials be analyzed to test our hypothesis. Methanol 

is a polar organic solvent and would be expected to dissolve 

large amounts of polar organic compounds, such as acetone 

and MEK, as well as lesser amounts of less polar and nonpolar 

organic compounds. The methanol used for cleaning is not 

certified as being free of other organic constituents and may be 

exposed to airborne contaminants while being transferred into 

the containers used to transport it safely in the mobile laboratories, while being stored in the mobile laboratories, and while 

being used for cleaning. Thus, the methanol likely had many 

opportunities to accumulate organic contaminants.

The laboratory analyzed all three vials for VOCs and 

the three vials yielded different results. For the purposes of 

discussion, the vials are numbered based on the size of an 

unusual peak present on the chromatograms for all three vials 

from this field blank; this peak is not present on chromatograms for groundwater or surface-water samples (Donna 

Rose, U.S. Geological Survey, written commun., 2007). The 

chromatogram for the first vial had a large, broad peak near 

the beginning of the chromatogram. On the basis of comparison between retention times for identified VOCs on the 

chromatogram and retention times for a larger suite of VOCs 

(J&W Scientific, 1998), this large, broad peak was inferred to 

correspond to methanol. The size of the methanol peak 

systematically decreased from the first to the second to the 

third vial. 
70 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

The analytical results for the first, second, and third 

vials also showed a progressive decrease in the number and 

concentration of VOCs detected (table A3B). In addition, the 

laboratory reported an unusually high number of tentatively 

identified compounds (TIC) in the chromatogram of the first 

vial, and fewer TICs in the chromatograms for the second and 

third vials (table A3B). TICs are constituents not included in 

the 85 VOCs analyzed on NWQL schedule 2020. TICs are 

tentatively identified on the basis on their retention times and 

their mass spectra. The presence of a large number of TICs 

suggests some VOCs in the sample may have come from a 

source that usually does not contribute VOCs to groundwater 

or surface-water samples (NWQL schedule 2020 was designed 

to include most VOCs encountered in groundwater or surfacewater samples [Connor and others, 1998]).

On the basis of these results, residual methanol from 

cleaning of equipment was inferred to be the source of the 

VOC detections in the three vials of this field blank. The 

progressive changes in the size of the inferred methanol peak, 

the number of TICs, and the number and concentration of 

VOCs detected from the first to the second to the third vial 

are inferred to reflect the progressive decrease in the amount 

of methanol in the blank water as the pump was flushed with 

more blank water. Results from the third vial were used to 

represent the field blank and are included in table A3A. Results 

from the third vial indicated detections of MEK and toluene 

in the field blank (table A3A,B). MEK was not detected in 

any groundwater samples from the Tahoe–Martis study unit 

(table 5); thus it is unlikely that methanol used for the cleaning 

procedures contaminated any of the groundwater samples. 

Tetrahydrofuran was not detected in any field blanks or 

source-solution blanks, but it was detected in two groundwater 

samples at concentrations of 1 and 9 μg/L. Tetrahydrofuran 

was the only solvent detected in either groundwater sample, 

which is unusual. The field notes and photographs showed that 

in both sites, the groundwater passed through fairly new PVC 

piping between the well-head and the sampling point, and the 

piping had several joints sealed with PVC cement. Tetrahydrofuran is a main ingredient in PVC cement; thus, it is likely that 

the tetrahydrofuran in the groundwater samples came from 

the cement. Both detections of tetrahydrofuran were V-coded 

and excluded from the dataset of groundwater quality results 

(tables 5 and A3A).

Six field blanks were analyzed for pesticide compounds 

and there were no detections.

Two laboratories analyzed field blanks for NDMA and 

perchlorate, Montgomery Watson Harza laboratory (MWH) 

and Weck laboratory (Weck). NDMA was detected in one 

of the four field blanks analyzed by MWH at a concentration of 0.0033 μg/L and was not detected in either of the two 

field blanks analyzed by Weck (table A3A). NDMA was not 

detected in any of the 10 groundwater samples analyzed. Six 

field blanks were analyzed for perchlorate by MWH and two 

field blanks were analyzed for perchlorate Weck laboratory; 

perchlorate was not detected in any of the field blanks.

Of the six field blanks analyzed for nutrients, one 

contained E0.013 mg/L of ammonia and another contained 

E0.003 mg/L of orthophosphate (table A3A). Two groundwater samples had orthophosphate concentrations less than 

or equal to 0.006 mg/L (E0.003 mg/L plus one-half the LRL 

of 0.006 mg/L) and were flagged with a ≤ symbol. (table 7). 

Three groundwater samples had ammonia concentrations 

less than 0.023 mg/L (E0.013 mg/L plus one-half the LRL 

of 0.02 mg/L) and were flagged with a ≤ symbol. The ≤ flag 

indicates that the true concentration in the groundwater sample 

is less than or equal to the measured concentration, including 

the possibility that the true concentration may have been less 

than the LRL and thus reported as a nondetection.

Six field blanks and six source-solution blanks were 

analyzed for major ions. One field blank had a total dissolved 

solids (TDS) concentration of 10 mg/L (table A3A). However, 

the only other constituents detected in this field blank were 

silica (0.02 mg/L), MEK (4.1 μg/L), and radium-226 (0.042 + 

0.013 pCi/L), which together account for less than 1 percent of 

the measured TDS. No TDS results for groundwater samples 

were flagged. Five field blanks had concentrations of silica 

ranging from 0.02 to 0.43 mg/L (table A3A). The lowest concentration measured in groundwater was 9.51 mg/L (table 8), 

which is greater than 0.044 mg/L (0.43 mg/L plus one-half the 

LRL of 0.018 mg/L), thus no groundwater data were flagged.

The GAMA study reporting limits (SRL), instead of 

the results for the six field blanks collected at Tahoe–Martis 

sites, were used to determine which trace element data should 

be flagged; SRLs are based on the results for 86 field blanks 

collected between May 2004 and January 2008 (L.D. Olsen 

and M.S. Fram, U.S. Geological Survey, unpub. data, 2008). 

Aluminum, barium, chromium, copper, iron, lead, manganese, 

nickel, tungsten, vanadium, and zinc have SRLs. Measured 

values that are less than the SRL are flagged with a ≤ symbol 

in table 9. Of these 11 trace elements, only aluminum and 

nickel were detected in field blanks collected at Tahoe–

Martis sites (table A3A). Nickel was detected in one field 

blank at a concentration of E0.04 μg/L, which is less than the 

SRL of 0.36 μg/L. Aluminum was detected in one field blank 

at a concentration of 4 μg/L, which is greater than the SRL of 

1.6 μg/L. Aluminum was detected in the associated sourcesolution blank also at a concentration of 4.2 μg/L. Although 

concentrations of aluminum detected in 9 groundwater 

samples are less than 4 μg/L but greater than 1.6 μg/L, these 

detections have not been flagged with a ≤ symbol because the 

SRL was used to determine which data should be flagged.

Six field blanks were analyzed for arsenic, iron, and 

chromium by the USGS Trace Metals laboratory in Boulder, 

Colorado. One field blank contained 0.79 μg/L of arsenic and 

another contained 3 μg/L of iron (table A3A). Two concentrations of arsenic detected in groundwater samples and three 

of iron were less than the concentration detected in the field 

blank and were flagged with a ≤ symbol (table 10).
Appendix 71

Four field blanks and four source-solution blanks were 

analyzed for radioactive constituents. Three field blanks and 

their associated source solution blanks had detections of 

radium-226; the maximum activity was 0.042 ± 0.013 pCi/L 

(table A3A). Seven groundwater samples had radium-226 

activities less than 0.055 pCi/L, the upper confidence limit 

of the maximum activity measured in a blank. These data 

were flagged with a ≤ symbol (table 12). One field blank 

had a gross alpha particle activity (72-hour count) of 0.54 ± 

0.33 pCi/L. The lowest gross alpha particle activity (72-hour 

count) measured in groundwater was 1.04 + 0.71 pCi/L; thus 

no data were flagged (table 12B).

Variability in Replicate Samples

Tables A4A-C summarize the results of replicate analyses 

for constituents detected in groundwater samples collected in 

the Tahoe–Martis study. Replicate analyses were made on 12 

percent of the samples collected. Of the 1,320 replicate pairs 

analyzed (counted by constituent), 414 were analyzed for 

constituents detected in at least one groundwater sample. Of 

these 414 pairs, 12 had results outside the limits for acceptable 

precision. Results for replicate analyses for constituents that 

were not detected are not reported in tables A4A–C. 

Six replicate pairs of samples were analyzed for organic 

constituents and nearly all pairs yielded two values reported as 

nondetections (table A4A). One replicate pair for 1,2,4-

trimethylbenzene and one for tetrahydrofuran each yielded 

two V-coded values. Variability was not assessed for pairs with 

V-coded data because the data are not considered representative of the composition of the groundwater. One replicate pair 

for carbon disulfide yielded two detections, and the SD of the 

concentrations was 0.15 μg/L, which was greater than onehalf the LRL of 0.06 μg/L for carbon disulfide. An E-code was 

assigned to the one carbon disulfide detection in a groundwater sample to indicate greater uncertainty in the magnitude of 

the reported concentration (table 5).

Six replicate pairs of samples were analyzed for major 

and minor ions, nutrients, trace elements, trace element species, and isotopic tracers. Over 97 percent of the pairs yielded 

two concentrations with an SD value of less than 1⁄2 the LRL 

(for concentrations <5 LRL), an RSD value of less than 10 

percent (for concentrations ≥5 LRL), or two nondetections 

(table A4B). These results indicated data for groundwater 

samples from the Tahoe–Martis study unit had variability 

within acceptable ranges.

One replicate pair analyzed for boron yielded concentrations with an RSD value greater than 10 percent; this sample 

(TROCK-12) was diluted during analysis to reduce matrix 

interferences. Diluting a sample requires mixing measured 

aliquots of blank water and sample water and measurement 

error may have increased variability between results for the 

replicate pair. One replicate pair analyzed for iron yielded one 

detection and one nondetection (TTAHOU-02). However, the 

concentration detected in the replicate was 10 μg/L, which 

was less than one-tenth of the SMCL-CA for iron. The lessthan-acceptable precision at this low concentration will not 

affect the assessments of groundwater quality being made by 

the GAMA Priority Basin Project.

Four replicate pairs were analyzed for species of iron 

and arsenic by the USGS Trace Metals Laboratory in Boulder, Colorado. One replicate pair analyzed for species of iron 

yielded a detection and a nondetection for both total iron and 

iron(II) (table A4B). The USGS NWQL reported that iron was 

not detected in this sample (TTAHO-02; table 9), and USGS 

NWQL results are preferred (table A2).

Six replicate pairs of samples were analyzed for uranium 

isotopes, tritium, and radon, and two pairs were analyzed for 

radium isotopes and gross alpha and gross beta particle activities (table A4C). Eighty-three percent of the replicate pairs 

yielded overlapping values and were therefore considered 

acceptable. One replicate pair each analyzed for uranium-234, 

uranium-235, radium-228 and gross alpha particle activity 

(72-hour count) and two replicate pairs for radon and gross 

alpha particle activity (72-hour count) yielded non-overlapping values. However, the activities were less than one-third 

of the activities of the corresponding MCL-CA, MCL-US, and 

proposed AMCL-US values (table 3I). The less-than-acceptable precision for these constituents at these low activities will 

not affect the assessments of groundwater quality being made 

by the GAMA Priority Basin Project.

One replicate pair analyzed for radium-228 yielded nonoverlapping values, and had one activity that was more than 

half of the activity of the corresponding MCL-US. However, 

this sample (TTAHO-11) was the only sample in which 

radium-228 was detected (table 12C); thus no samples were 

incorrectly reported as having activities above the MCL-US. 

One replicate pair analyzed for gross alpha particle activity 

(72-hour count) yielded non-overlapping values; the sample 

had an activity greater than the MCL-US and the replicate had 

an activity less than the MCL-US (table A4C). However, the 

groundwater sample (TTAHO-11) was analyzed 1 day beyond 

the 72-hour holding time (table 12B), and the replicate sample 

was analyzed 4 days beyond the 72-hour holding time. Decay 

of alpha-emitting species with short half-lives may account 

for the decrease in gross alpha particle activity between the 

time the groundwater sample and the replicate sample were 

analyzed.

Perchlorate was analyzed in quadruplicate at one Tahoe–

Martis site. Perchlorate was not detected in the groundwater 

and replicate samples analyzed by Weck nor was it detected in 

the replicate sample analyzed by MWH. However, perchlorate 

was detected at a concentration of 11 μg/L in the groundwater sample analyzed by MWH. Because perchlorate was not 

detected in three analyses and was detected at a high concentration in only one analysis, the detection was V-coded and 

excluded from the dataset of groundwater quality results.
72 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Fourteen additional samples were analyzed for perchlorate by both MWH and Weck. Both laboratories reported the 

no perchlorate was detected in 13 of the 14 samples. In one 

sample (TTAHOU-04), Weck detected perchlorate and MWH 

did not. However, the concentration of perchlorate reported by 

Weck, 0.13 μg/L, was less than the detection limit of 0.5 μg/L 

used by MWH.

Matrix-Spike Recoveries

Tables A5A,B summarize the results of matrix-spike 

recovery tests for the Tahoe–Martis study. Adding a spike (a 

known concentration of a compound) to an environmental 

sample enables the analyzing laboratory to determine the 

effect of the matrix, in this case groundwater, on the analytical 

technique used to measure the compound. Six groundwater 

samples were spiked with VOCs to calculate matrix-spike 

recoveries (table A5A). Acceptable results for matrix-spike 

recovery tests were defined as recoveries between 70 and 

130 percent. The median recoveries for all 88 VOC compounds were within this acceptable range. Three VOC 

compounds yielded a least one matrix-spike recovery greater 

than 130 percent. Of these three compounds, only 1,2,4-trimethylbenzene was detected in groundwater samples, and all 

detections of 1,2,4-trimethylbenzene were V-coded because 

it was detected in the field and source-solution blanks. One 

compound, hexachlorobutadiene, had at least one matrix-spike 

recovery less than 70 percent, but was not detected in groundwater samples. [NOTE that low recoveries may indicate that 

the compound might not have been detected in some samples 

if it was present at very low concentrations].

Six groundwater samples were spiked with pesticide and 

pesticide degradate compounds in order to calculate matrixspike recoveries (table A5B). Acceptable results for matrixspike recovery tests were defined as recoveries between 70 

and 130 percent. The median recoveries for 40 of the 

62 compounds were within this acceptable range. All 62 

compounds had at least one matrix-spike recovery less than 

70 percent, and 11 compounds had median recoveries less than 

70 percent. For nine compounds all six matrix-spike recovery 

tests yielded recoveries less than 70 percent. Two of those 

compounds, deethyatrazine and dicrotofos, were detected in 

groundwater samples (table 6). [NOTE that low recoveries 

may indicate that the compound might not have been detected 

in some samples if it was present at very low concentrations]. 

Ten compounds had at least one matrix-spike recovery greater 

than 130 percent, but none of these compounds were detected 

in groundwater samples.

Two groundwater samples were spiked with NDMA in 

order to calculate matrix-spike recovery. Acceptable results 

for matrix-spike recovery tests were defined as recoveries 

between 70 and 130 percent, and the tests yielded spike recoveries of 98 and 112 percent.

Surrogate Compound Recoveries

Surrogate compounds were added to samples in the 

laboratory and analyzed to evaluate the recovery of similar constituents. Table A6 lists the surrogate, the analytical 

schedule on which it was applied, the number of analyses of 

blanks and of groundwater samples (environmental samples, 

replicates, and matrix-spike samples), the number of surrogate recoveries below 70 percent and the number of surrogate recoveries above 130 percent for the blanks and the 

groundwater samples. Blank and groundwater samples were 

considered separately to assess whether the matrices present in 

groundwater samples affect surrogate recoveries. The results 

suggest that the presence of sample matrices may decrease the 

recovery of 1-bromo-4-fluorobenzene and increase the recovery of 1,2-dichloroethane-d4 (table A6). However, because the 

median matrix-spike recoveries of all VOC compounds were 

within acceptable ranges, this change in surrogate recovery 

apparently did not have a noticeable effect on the data. Eightytwo percent of the surrogate recoveries for VOC and gasoline 

oxygenate and degradate compounds, and 95 percent of the 

surrogate recoveries for pesticide compounds were in the 

acceptable ranges.
Appendix Tables 73

Appendix Tables
74 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table A1. Analytical methods used to measure organic, inorganic, and microbial constituents by the U.S. Geological Survey (USGS) 

National Water Quality Laboratory (NWQL) and other laboratories.—Continued

[Laboratory entity codes in the USGS National Water Information System (NWIS) for laboratories other than the USGS National Water Quality Laboratory 

(NWQL) are given in parentheses after the laboratory names. VOC, volatile organic compound; HPLC, high-performance liquid chromatography]

Analyte Analytical method Laboratory and analytical 

schedule Citation(s)

Water-quality indicators

Field parameters Calibrated field meters and test 

kits

USGS field measurement U.S. Geological Survey, 

variously dated

Organic constituents

VOCs Purge and trap capillary gas 

chromatography/mass spectrometry

NWQL, Schedule 2020 Connor and others, 1998

Pesticides and degradates Solid-phase extraction and gas 

chromatography/mass spectrometry

NWQL, Schedule 2003 Zaugg and others, 1995; Lindley 

and others, 1996; Madsen and 

others, 2003; Sandstrom and 

others, 2001

Gasoline oxygenates Heated purge and trap/gas chromatography/mass spectrometry NWQL, Schedule 4024 Rose and Sandstrom, 2003

Pharmaceuticals Solid-phase extraction and 

HPLC/mass spectrometry

NWQL, Schedule 2080 Furlong and others, 2008

Constituents of special interest

Perchlorate Ion chromatography and mass 

spectrometry 

Montgomery Watson Harza 

Laboratory (CA-MWHL)

Hautman and others, 1999

N-Nitrosodimethylamine 

(NDMA)

Gas chromatography and mass 

spectrometry 

Montgomery Watson Harza 

Laboratory (CA-MWHL)

U.S. Environmental Protection 

Agency, 2004; U.S. Environmental Protection Agency, 

1999b

Perchlorate Liquid chromatography electrospray ionization mass 

spectrometry

Weck Laboratory U.S. Environmental Protection 

Agency, 2005

N-Nitrosodimethylamine 

(NDMA)

Gas chromatography and mass 

spectrometry 

Weck Laboratory U.S. Environmental Protection 

Agency, 2004; Plomley and 

others, 1994

Inorganic constituents

Nutrients Alkaline persulfate digestion, 

Kjedahl digestion

NWQL, Schedule 2755 Fishman, 1993; Patton and 

Kryskalla, 2003

Major and minor ions, trace elements and nutrientsAtomic absorbance spectroscopy, 

colorimetry, ion-exchange 

chromatography, inductivelycoupled plasma atomic emission spectrometry and mass 

spectrometry

NWQL, Schedule 1948 Fishman and Friedman, 1989; 

Fishman, 1993; Faires, 1993; 

McLain, 1993; Garbarino, 

1999; Garbarino and Damrau, 

2001; American Public Health 

Association, 1998; Garbarino 

and others, 2006

Chromium, arsenic and iron 

speciation

Various techniques of ultraviolet 

visible (UV-VIS) spectrophotometry and atomic absorbance spectroscopy

USGS Trace Metal Laboratory, 

Boulder, Colorado 

(USGSTMCO)

Stookey, 1970; To and others, 

1998; Ball and McCleskey, 

2003a,b; McCleskey and others, 2003

Table A1. Analytical methods used to measure organic, inorganic, and microbial constituents by the U.S. Geological Survey (USGS) 

National Water Quality Laboratory (NWQL) and other laboratories.

[Laboratory entity codes in the USGS National Water Information System (NWIS) for laboratories other than the USGS National Water Quality Laboratory 

(NWQL) are given in parentheses after the laboratory names. VOC, volatile organic compound; HPLC, high-performance liquid chromatography]
Appendix Tables 75

Table A1. Analytical methods used to measure organic, inorganic, and microbial constituents by the U.S. Geological Survey (USGS) 

National Water Quality Laboratory (NWQL) and other laboratories.—Continued

[Laboratory entity codes in the USGS National Water Information System (NWIS) for laboratories other than the USGS National Water Quality Laboratory 

(NWQL) are given in parentheses after the laboratory names. VOC, volatile organic compound; HPLC, high-performance liquid chromatography]

Analyte Analytical method Laboratory and analytical 

schedule Citation(s)

Isotope tracers

Stable isotopes of hydrogen and 

oxygen in water

Gaseous hydrogen and carbon 

dioxide-water equilibration 

and stable-isotope mass 

spectrometry

USGS Stable Isotope Laboratory, 

Reston, Virginia (USGSSIVA), 

NWQL Schedule 1142

Epstein and Mayeda, 1953; 

Coplen and others, 1991; 

Coplen, 1994

Strontium isotopes Chemical separations and 

thermal-ionization mass 

spectrometry

USGS Radiogenic Isotope 

Laboratory, Menlo Park, 

California

Bullen and others, 1996

Carbon isotopes Accelerator mass spectrometry University of Waterloo, 

Environmental Isotope 

Laboratory (CAN-UWIL); 

University of Arizona 

Accelerator Mass 

Spectrometry Laboratory 

(AZ-UAMSL), NWQL 

Schedule 2015

Donahue and others, 1990; Jull 

and others, 2004

Radioactivity and gases

Tritium Electrolytic enrichment-liquid 

scintillation

USGS Stable Isotope and Tritium 

Laboratory, Menlo Park, 

California (USGSH3CA)

Thatcher and others, 1977

Tritium and noble gases Helium-3 in-growth and mass 

spectrometry

Lawrence Livermore National 

Laboratory (CA-LLNL)

Moran and others, 2002; Eaton 

and others, 2004

Radon-222 Liquid scintillation counting NWQL, Schedule 1369 American Society for Testing 

and Materials, 1998

Radium isotopes Alpha activity counting Eberline Analytical Services 

(CA-EBERL), NWQL 

Schedule 1262 

Kreiger and Whittaker, 1980 

(USEPA methods 903.0 and 

903.1)

Uranium isotopes Chemical separations and 

alpha-particle spectrometry

 Eberline Analytical Services 

(CA-EBERL), NWQL 

Schedule 1130 

American Society for Testing 

and Materials, 2002

Gross alpha and beta 

radioactivity

Alpha and beta activity counting Eberline Analytical Services, 

NWQL Schedule 1792

Kreiger and Whittaker, 1980 

(USEPA method 900.0)

Microbial constituents

F-specific and somatic coliphage Single-agar layer (SAL) and 

two-step enrichment methods

USGS Ohio Water Microbiology 

Laboratory (USGSOHML)

U.S. Environmental Protection 

Agency, 2001
76 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table A2. Preferred analytical schedules for constituents appearing on multiple schedules for samples collected for the Tahoe–Martis 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.

[Of the methods used to analyze the compound in question, analytical schedules that are the most accurate and precise usually are preferred except when consistency with historic data analyzed using the same method is preferred. Laboratory: LLNL, Lawrence Livermore National Laboratory; MWH, Montgomery Watson Harza Laboratory; SITL, U.S. Geological Survey Stable Isotope and Tritium Laboratory; TML, U.S. Geological Survey Trace Metal Laboratory, Boulder, 

Colorado; Weck, Weck Laboratory. Other abbreviations: VOC, volatile organic compound; —, no preference]

Constituent Primary constituent 

classification Analytical schedules Preferred analytical schedule

Results from preferred method reported

Acetone VOC, gasoline additive degradate 2020, 4024 2020

tert-Amyl methyl ether (TAME) VOC, gasoline oxygenate 2020, 4024 2020

Diisopropyl ether (DIPE) VOC, gasoline oxygenate 2020, 4024 2020

Ethyl tert-butyl ether (ETBE) VOC, gasoline oxygenate 2020, 4024 2020

Methyl tert-butyl ether (MTBE) VOC, gasoline oxygenate 2020, 4024 2020

Results from both methods reported

Alkalinity Water-quality indicator Field, 1948 Field

Arsenic, total Trace element 1948, TML 1948

Chromium, total Trace element 1948, TML 1948

Iron, total Trace element 1948, TML 1948

pH Water-quality indicator Field, 1948 Field

Specific conductance Water-quality indicator Field, 1948 Field

Perchlorate Special interest MWH, Weck MWH

N-Nitrosodimethylamine Special interest MWH, Weck MWH

Tritium Isotope tracer LLNL, SITL —
Appendix Tables 77

Table A3A. Constituents detected in field blanks collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June–September 2007.

[V-coded data for groundwater samples are excluded from the dataset of groundwater quality results because the constituents were detected in blanks at similar 

concentrations or were determined to be a result of contamination during sample collection. Abbreviations: E, estimated value; pCi/L, picocurie per liter; mg/L, 

milligram per liter; μg/L, microgram per liter; —, not detected; ≤, less than or equal to; ±, plus or minus]

Constituent Number of field blank 

detections/analyses

Concentrations detected 

in field blanks

Number of groundwater 

samples V-coded or ≤-coded

Organic constituents (μg/L)

Toluene 2/6 E0.02, E0.02 2

Methyl ethyl ketone (2-butanone, MEK) 1/6 E4.1 0

Tetrahydrofuran 0/6 — 2

1,2,4-Trimethylbenzene1 3/6 E0.05, E0.05, 0.12 20

NDMA 1/4 0.0033 0

Nutrients and major ions (mg/L)

Ammonia, as nitrogen 1/6 E0.013 3

Orthophosphate, as phosphorus 1/6 E0.003 2

Silica 5/6 0.02, 0.04, 0.43, 0.03, 0.03 0

Total dissolved solids (TDS) 1/6 10 0

Trace elements (μg/L)

Aluminum2,3 1/6 4 15

Chromium3 0/6 — 24

Copper3 0/6 — 34

Lead3 0/6 — 39

Manganese3 0/6 — 5

Nickel3 1/6 E0.04 26

Tungsten3 0/6 — 10

Vanadium3 0/6 — 2

Zinc3 0/6 — 27

Arsenic (total)4 1/6 0.79 3

Iron (total)4 1/6 3 3

Radioactivity (pCi/L)

Gross alpha, 72-hour count 1/4 0.54 ± 0.33 0

Radium-2265 3/4 0.0013 ± 0.0070, 

0.017 ± 0.011, 

0.042 ± 0.013

7

1

1,2,4-Trimethylbenzene was also detected in 1 of 3 source-solution blanks at a concentration of E0.03 μg/L.

2

Aluminum was detected in the associated source-solution blank at a concentration of 4.2 μg/L. Calcium was detected in the same source-solution blank at a 

concentration of E0.01 mg/L.

3

Constituents have a study reporting limit (SRL) defined based on examination of GAMA quality-control samples collected from May 2004 through January 

2008 (L.D. Olsen and M.S. Fram, U.S. Geological Survey, unpub. data, 2008).

4

Constituents analyzed by the USGS Trace Metal Laboratory in Boulder, Colorado using research methods.

5

Radium-226 was detected in 3 of 4 source-solution blanks at concentrations of 0.023 ± 0.010, 0.029 ± 0.012, 0.030 ± 0.011 pCi/L, respectively.
78 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table A3B. Volatile organic compounds (VOC) detected in a 

field blank analyzed in triplicate and determined to be affected by 

residual methanol from equipment cleaning.

[The three vials were collected sequentially. TICs, tentatively identified compounds; E, estimated value; μg/L, microgram per liter; —, not detected]

Constituent Concentration (μg/L)

Vial #1 Vial #2 Vial #3

Acetone 30.3 E3.4 —

Methyl ethyl ketone 

(MEK)

155 16.4 E4.1

Tetrahydrofuran 4.36 E0.64 —

Toluene 0.12 E0.02 E0.02

Ethylbenzene E0.07 E0.01 —

m- and p-Xylenes E0.20 E0.06 —

o-Xylene E0.08 E0.02 —

Styrene E0.05 — —

1,2,4-Trimethylbenzene E0.02 — —

TICs 13 0 1
Appendix Tables 79

Table A4A. Quality-control summary of replicate analyses of organic constituents detected in samples collected for the Tahoe–Martis 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.

[SD, standard deviation; RSD, percent relative standard deviation; LRL, laboratory reporting limit; μg/L, microgram per liter; V, analyte detected in samples and 

blanks thus result is not considered a detection for groundwater quality assessment; —, none in category; nv, no values in category]

Constituent

Number of 

nondetects/number 

of replicates

Number of 

V-coded 

replicates

Number of SDs 

greater than 

1⁄2 LRL/number of 

replicates with 

concentration less 

than 5 times 

the LRL

Concentrations of 

replicates with SDs 

greater than 

1⁄2 LRL 

(environmental, 

replicate) 

Number of RSDs 

greater than 

ten percent/

number of replicates 

with concentration 

greater than 

5 times the LRL

Volatile organic compounds and gasoline oxygenates (Schedules 2020 and 4204)

Chloroform 6/6 — — nv —

Perchloroethene 6/6 — — nv —

Bromodichloromethane 6/6 — — nv —

Methyl tert-butyl ether 6/6 — — nv —

Trichloroethene 6/6 — — nv —

1,1,1-Trichloroethane 6/6 — — nv —

Diisopropyl ether 6/6 — — nv —

Carbon disulfide 5/6 — 1/6 0.35, 0.14 —

1,2,4-Trimethylbenzene 5/6 1 — nv —

Tetrahydrofuran 5/6 1 — nv —

Toluene 6/6 — — nv —

Pesticides and pesticide degradates (Schedule 2003)

Atrazine 6/6 — — nv —

Deethylatrazine 6/6 — — nv —

Dicrotophos 6/6 — — nv —
80 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table A4B. Quality-control summary of replicate analyses of major and minor ions, nutrients, trace elements, and isotope tracers 

detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

June–September 2007.—Continued

[SD, percent standard deviation; RSD, percent relative standard deviation in percent; LRL, laboratory reporting limit; USGS, U.S. Geological Survey; δ2H, 

delta hydrogen; δ18O, delta oxygen; δ13C, delta carbon; Sr, strontium. μg/L, microgram per liter; mg/L, milligram per liter; per mil, per thousand; nv, no measured values in category; —, none in category; <, less than]

Constituent

Number of 

non-detected 

or ≤-coded 

replicates

Number of SDs 

greater than 

1⁄2 LRL/number 

of replicates 

with concentration 

less than 5 times 

the LRL

Concentrations of 

replicates with 

SDs greater than 

1⁄2 LRL 

(environmental, 

replicate) 

Number of RSDs 

greater than 

ten percent/number 

of replicates 

with concentration 

greater than 

5 times the LRL

Concentrations 

of replicates 

with RSDs greater 

than ten percent 

(environmental, 

replicate) 

Major and minor Ions (mg/L)

Alkalinity — — nv 0/6 nv

Calcium — — nv 0/6 nv

Magnesium — — nv 0/6 nv

Potassium — 0/1 nv 0/5 nv

Sodium — — nv 0/6 nv

Bromide 4 0/1 nv 0/1 nv

Chloride — 0/2 nv 0/4 nv

Fluoride 3 0/1 nv 0/2 nv

Iodide 3 0/1 nv 0/2 nv

Sulfate — 0/2 nv 0/4 nv

Silica — — nv 0/6 nv

Total dissolved solids — — nv 0/6 nv

Nutrients (mg/L)

Phosphorus — 0/1 nv 0/5 nv

Total nitrogen 2 0/4 nv — nv

Nitrate plus nitrite 4 0/2 nv — nv

Ammonia 3 0/3 nv — nv

Nitrite 3 0/3 nv — nv

Trace elements (μg/L)

Aluminum 3 0/2 nv 0/1 nv

Antimony 4 0/2 nv — nv

Arsenic — 0/2 nv 0/4 nv

Barium — — nv 0/6 nv

Beryllium 4 0/1 nv 0/1 nv

Boron 1 1/2 nv 1/3 (84, 152)

Cadmium 4 0/2 nv — nv

Chromium 4 0/1 nv 0/1 nv

Cobalt — 0/4 nv 0/2 nv

Copper 4 1/1 nv 0/1 nv

Iron 2 1/1 (<6, 10) 0/3 nv

Lead 5 — nv 0/1 nv

Lithium — 1/2 nv 0/4 nv

Manganese 2 — nv 0/4 nv

Molybdenum 1 0/2 nv 0/3 nv

Nickel 4 — nv 0/2 nv

Selenium 4 0/2 nv — nv

Strontium — — nv 0/6 nv

Table A4B. Quality-control summary of replicate analyses of major and minor ions, nutrients, trace elements, and isotope tracers 

detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–

September 2007.

[SD, percent standard deviation; RSD, percent relative standard deviation in percent; LRL, laboratory reporting limit; USGS, U.S. Geological Survey; δ2H, delta 

hydrogen; δ18O, delta oxygen; δ13C, delta carbon; Sr, strontium. μg/L, microgram per liter; mg/L, milligram per liter; per mil, per thousand; nv, no measured 

values in category; —, none in category; <, less than]
Appendix Tables 81

Table A4B. Quality-control summary of replicate analyses of major and minor ions, nutrients, trace elements, and isotope tracers 

detected in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

June–September 2007.—Continued

[SD, percent standard deviation; RSD, percent relative standard deviation in percent; LRL, laboratory reporting limit; USGS, U.S. Geological Survey; δ2H, 

delta hydrogen; δ18O, delta oxygen; δ13C, delta carbon; Sr, strontium. μg/L, microgram per liter; mg/L, milligram per liter; per mil, per thousand; nv, no measured values in category; —, none in category; <, less than]

Constituent

Number of 

non-detected 

or ≤-coded 

replicates

Number of SDs 

greater than 

1⁄2 LRL/number 

of replicates 

with concentration 

less than 5 times 

the LRL

Concentrations of 

replicates with 

SDs greater than 

1⁄2 LRL 

(environmental, 

replicate) 

Number of RSDs 

greater than 

ten percent/number 

of replicates 

with concentration 

greater than 

5 times the LRL

Concentrations 

of replicates 

with RSDs greater 

than ten percent 

(environmental, 

replicate) 

Thallium 6 — nv — nv

Tungsten 3 — nv 0/3 nv

Uranium 1 0/2 nv 0/3 nv

Vanadium 2 — nv 0/4 nv

Zinc 3 — nv 0/3 nv

USGS Boulder, Colorado, Trace Metals Laboratory (μg/L)

Iron(total) 2 — nv 1/2 (<2, 16)

Iron(II) 2 1/1 (<2, 5) 0/1 nv

Arsenic(total) 2 — nv 0/2 nv

Arsenic(III) 2 — nv 0/2 nv

Isotope tracers

δ2

H (per mil) — — nv 0/6 nv

δ18O (per mil) — — nv 0/6 nv

δ13C (per mil) — — nv 0/6 nv

Carbon-14 (percent modern) — — nv 0/6 nv

87Sr/86Sr (atom ratio) — — nv 0/6 nv
82 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table A4C. Quality-control summary of replicate analyses of radiochemical constituents detected in samples collected for the Tahoe–

Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.

[pCi/L, picocurie per liter; nv, no values with non-overlapping ranges]

Constituent Number of non-overlapping 

values/number of replicates

Activities for replicates 

with non-overlapping values 

(environmental, replicate) 

(pCi/L)

Uranium-234 1/6 (0.474 ± 0.014, 0.366 ± 0.033)

Uranium-235 1/6 (0.049 ± 0.014, 0.020 ± 0.012)

Uranium-238 0/6 nv

Radon-222 2/6 (780 ± 13, 820 ±14), (1210 ± 17, 1100 ± 16)

Radium-226 0/2 nv

Radium-228 1/2 (3.04 ± 0.15, 2.68 ± 0.14)

Gross alpha particle activity, 72-hr count 2/2 (1.21 ± 0.91, 3.4 ± 1.1), (26.2 ± 4.6, 10.0 ± 3.4)

Gross alpha particle activity, 30-day count 1/2 nv

Gross beta particle activity, 72-hr count 0/2 nv

Gross beta particle activity, 30-day count 0/2 nv

Tritium 0/6 nv
Appendix Tables 83

Table A5A. Quality-control summary of matrix-spike recoveries of volatile organic compounds (VOC) and gasoline oxygenates and 

degradates in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

June–September 2007.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number 

of spike 

samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acetone1 6 95 115 109

Acrylonitrile 6 95 112 104

tert-Amyl alcohol 3 94 98 97

tert-Amyl ethyl ether (TAME)1 6 84 106 101

Benzene 6 97 112 100

Bromobenzene 6 96 113 103

Bromochloromethane 6 94 109 103

Bromodichloromethane2 6 94 117 105

Bromoform (tribromomethane) 6 94 122 102

Bromomethane (Methyl bromide) 6 80 143 103

tert-Butyl alcohol (TBA) 3 92 98 97

n-Butylbenzene 6 80 121 93

sec-Butylbenzene 6 93 111 102

tert-Butylbenzene 6 100 120 107

Carbon disulfide2 6 70 86 78

Carbon tetrachloride (tetrachloromethane) 6 98 122 110

Chlorobenzene 6 94 113 103

Chloroethane 6 83 120 105

Chloroform (trichloromethane)2 6 98 123 110

Chloromethane 6 88 109 91

3-Chloropropene 6 103 126 117

2-Chlorotoluene 6 96 113 101

4-Chlorotoluene 6 93 109 101

Dibromochloromethane 6 93 108 100

1,2-Dibromo-3-chloropropane (DBCP) 6 84 113 103

1,2-Dibromoethane (EDB) 6 97 118 103

Dibromomethane 6 94 110 102

1,2-Dichlorobenzene 6 94 113 99

1,3-Dichlorobenzene 6 92 111 98

1,4-Dichlorobenzene 6 93 108 96

trans-1,4-Dichloro-2-butene 6 92 124 98

Dichlorodifluoromethane (CFC-12) 6 79 99 87

1,1-Dichloroethane (1,1-DCA) 6 96 121 105

1,2-Dichloroethane (1,2-DCA) 6 91 116 106

1,1-Dichloroethene (1,1-DCE) 6 95 112 99

cis-1,2-Dichloroethene (cis-1,2-DCE) 6 96 117 108

trans-1,2-Dichloroethene (trans-1,2-DCE) 6 98 117 105

1,3-Dichloropropane 6 100 114 107

1,2-Dichloropropane 6 94 115 104

2,2-Dichloropropane 6 76 106 94

1,1-Dichloropropene 6 95 112 99

cis-1,3-Dichloropropene 6 82 109 92

trans-1,3-Dichloropropene 6 86 110 93

Diethyl ether 6 101 115 104

Diisopropyl ether (DIPE)1,2 6 96 113 103

Ethylbenzene 6 97 111 103

Ethyl tert-butyl ether (ETBE)1 6 91 125 101

Ethyl methacrylate 6 88 103 96

o-Ethyl toluene (1-ethyl-2-methyl benzene) 6 91 103 98

Hexachlorobutadiene 6 69 97 87

Hexachloroethane 6 90 113 102

Table A5A. Quality-control summary of matrix-spike recoveries of volatile organic compounds (VOC) and gasoline oxygenates and 

degradates in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

June–September 2007.

[Acceptable recovery range is between 70 and 130 percent]
84 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table A5A. Quality-control summary of matrix-spike recoveries of volatile organic compounds (VOC) and gasoline oxygenates and 

degradates in samples collected for the Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

June–September 2007.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number 

of spike 

samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

2-Hexanone (n-Butyl methyl ketone) 6 101 118 107

Iodomethane (Methyl iodide) 6 74 114 103

Isopropylbenzene 6 96 111 101

4-Isopropyl-1-methyl benzene 6 88 114 100

Methyl acetate 3 100 113 101

Methyl acrylate 6 95 110 105

Methyl acrylonitrile 6 97 116 108

Methyl tert-butyl ether (MTBE)1,2 6 91 120 104

Methyl iso-butyl ketone (MIBK) 6 93 115 105

Methylene chloride (dichloromethane) 6 89 111 97

Methyl ethyl ketone (2-butanone, MEK)3 6 93 113 106

Methyl methacrylate 6 80 115 96

Naphthalene 6 94 104 100

Perchloroethene (PCE)2 5 98 119 104

n-Propylbenzene 6 89 108 98

Styrene 6 95 105 102

1,1,1,2-Tetrachloroethane 6 93 113 105

1,1,2,2-Tetrachloroethane 6 90 110 106

Tetrahydrofuran3 6 101 126 108

1,2,3,4-Tetramethylbenzene 6 88 107 103

1,2,3,5-Tetramethylbenzene 6 92 125 106

Toluene3 6 96 114 98

1,2,3-Trichlorobenzene 6 97 109 100

1,2,4-Trichlorobenzene 6 85 101 94

1,1,1-Trichloroethane (1,1,1-TCA)2 6 100 124 111

1,1,2-Trichloroethane 6 93 113 100

Trichloroethene (TCE)2 6 92 115 97

Trichlorofluoromethane (CFC-11) 6 89 112 105

1,2,3-Trichloropropane (1,2,3-TCP) 6 99 131 107

Trichlorotrifluoroethane (CFC-113) 6 78 103 86

1,2,3-Trimethylbenzene 6 99 114 105

1,2,4-Trimethylbenzene3 6 97 139 105

1,3,5-Trimethylbenzene 6 93 111 101

Vinyl bromide (Bromoethene) 6 81 121 104

Vinyl chloride (Chloroethene) 6 95 121 104

m- and p-Xylene 6 99 111 105

o-Xylene 6 97 109 105

1

Constituents on schedules 2020 and 4024; only values from schedule 2020 are reported because it is the preferred analytical schedule.

2

Constituents detected in groundwater samples. 

3

Constituents detected in groundwater samples that were V-coded and excluded from the dataset of groundwater quality results because they were also 

detected in blanks.
Appendix Tables 85

Table A5B. Quality-control summary of matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acetochlor 6 55 133 107

Alachlor 6 56 132 107

Atrazine1 6 55 117 103

Azinphos-methyl 6 41 106 104

Azinphos-methyl-oxon 6 23 69 51

Benfluralin 6 34 90 66

Carbaryl 6 57 134 115

2-Chloro-2,6-diethylacetanilide 6 50 123 103

4-Chloro-2-methylphenol 6 57 93 74

Chlorpyrifos 6 43 119 97

Chlorpyrifos oxon 6 15 45 20

Cyfluthrin 6 28 108 71

Cypermethrin 6 30 88 70

Dacthal (DCPA) 6 49 127 102

Deethylatrazine1 6 35 67 58

Desulfinyl fipronil 6 43 122 90

Desulfinyl fipronil amide 6 45 126 98

Diazinon 6 51 109 98

3,4-Dichloroaniline 6 50 108 91

Dichlorvos 6 27 53 32

Dicrotophos1 6 31 64 44

Dieldrin 6 55 139 85

2,6-Diethylaniline 6 53 105 101

Dimethoate 6 24 49 41

Ethion 6 35 111 96

Ethion monoxon 6 40 111 103

2-Ethyl-6-methylaniline 6 57 100 97

Fenamiphos 6 43 109 101

Fenamiphos sulfone 6 37 106 84

Fipronil 6 49 139 105

Fipronil sulfide 6 37 127 94

Fipronil sulfone 6 31 90 75

Fonofos 6 49 108 92

Hexazinone 6 30 103 84

Iprodione 6 34 102 74

Isofenphos 6 51 119 109

Malaoxon 6 51 107 98

Malathion 6 50 139 109

Metalaxyl 6 60 127 108

Methidathion 6 42 117 101

Metolachlor 6 57 124 105

Table A5B. Quality-control summary of matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.

[Acceptable recovery range is between 70 and 130 percent]
86 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

Table A5B. Quality-control summary of matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Tahoe–Martis Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Metribuzin 6 49 105 92

Myclobutanil 6 46 117 111

1-Naphthol 6 20 45 38

Paraoxon-methyl 6 43 78 71

Parathion-methyl 6 52 117 90

Pendimethalin 6 48 125 92

cis-Permethrin 6 32 95 81

Phorate 6 43 87 67

Phorate oxon 6 55 149 96

Phosmet 6 7 47 25

Phosmet oxon 6 5 33 18

Prometon 6 52 128 103

Prometryn 6 58 135 111

Propyzamide 6 49 126 102

Simazine 6 57 120 107

Tebuthiuron 6 68 173 126

Terbufos 6 43 172 131

Terbufos oxon sulfone 6 49 113 92

Terbuthylazine 6 56 130 107

Tribufos 6 25 82 75

Trifluralin 6 40 100 75

1

Constituents detected in groundwater samples.
Appendix Tables 87

Table A6. Quality-control summary for surrogate recoveries of volatile organic compounds, gasoline oxygenates and degradates, 

pesticides and pesticide degradates, and constituents of special interest in samples collected for the Tahoe–Martis Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June–September 2007.

[MWH, Montgomery Watson Harza Laboratory; VOC, volatile organic compound; NDMA, N-nitrosodimethylamine]

Surrogate Analytical 

schedule

Constituent 

class 

analyzed

Number of 

analyses

Median 

recovery 

(percent)

Number 

of surrogate 

recoveries 

below 

70 percent

Number 

of surrogate 

recoveries 

above 

130 percent

Blanks

1-Bromo-4-fluorobenzene 2020, 4024 VOC, gasoline 9 88 0 0

1,2-Dichloroethane-d4 2020, 4024 VOC, gasoline 9 121 0 2

Isobutyl alcohol-d6 4024 Gasoline 2 105 0 0

Toluene-d8 2020, 4024 VOC, gasoline 9 100 0 0

Diazinon-d10 2003 Pesticide 6 90 1 0

α-HCH-d6 2003 Pesticide 6 87 1 0

NDMA-d6 MWH Special interest 6 82 0 2

Groundwater, replicate, and matrix-spike test samples

1-Bromo-4-fluorobenzene 2020, 4024 VOC, gasoline 65 77 12 0

1,2-Dichloroethane-d4 2020, 4024 VOC, gasoline 65 130 0 32

Isobutyl alcohol-d6 4024 Gasoline 26 95 0 0

Toluene-d8 2020, 4024 VOC, gasoline 65 98 0 0

Diazinon-d10 2003 Pesticide 64 95 2 0

α-HCH-d6 2003 Pesticide 64 86 3 0

NDMA-d6 MWH Special interest 13 85 2 0
88 Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program

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Manuscript approved for publication, February 25, 2009

Prepared by the USGS Publishing Network,

Publishing Service Center, Sacramento, California

For more information concerning the research in this report, contact the

California Water Science Center Director,

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Sacramento, California 95819

http://ca.water.usgs.gov
Printed on recycled paper

Fram and others—Groundwater Quality Data for the Tahoe–Martis Study Unit, 2007: Results from the California GAMA Program—Data Series 432